2562 строки
78 KiB
C
2562 строки
78 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion (tree-based version)
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* Internal non-public definitions that provide either classic
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* or preemptible semantics.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, you can access it online at
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* http://www.gnu.org/licenses/gpl-2.0.html.
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*
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* Copyright Red Hat, 2009
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* Copyright IBM Corporation, 2009
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*
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* Author: Ingo Molnar <mingo@elte.hu>
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* Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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*/
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#include <linux/delay.h>
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#include <linux/gfp.h>
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#include <linux/oom.h>
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#include <linux/sched/debug.h>
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#include <linux/smpboot.h>
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#include <uapi/linux/sched/types.h>
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#include "../time/tick-internal.h"
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#ifdef CONFIG_RCU_BOOST
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#include "../locking/rtmutex_common.h"
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/*
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* Control variables for per-CPU and per-rcu_node kthreads. These
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* handle all flavors of RCU.
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*/
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static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
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DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
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DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
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DEFINE_PER_CPU(char, rcu_cpu_has_work);
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#else /* #ifdef CONFIG_RCU_BOOST */
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/*
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* Some architectures do not define rt_mutexes, but if !CONFIG_RCU_BOOST,
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* all uses are in dead code. Provide a definition to keep the compiler
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* happy, but add WARN_ON_ONCE() to complain if used in the wrong place.
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* This probably needs to be excluded from -rt builds.
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*/
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#define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; })
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#endif /* #else #ifdef CONFIG_RCU_BOOST */
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#ifdef CONFIG_RCU_NOCB_CPU
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static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
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static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */
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static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
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#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
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/*
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* Check the RCU kernel configuration parameters and print informative
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* messages about anything out of the ordinary.
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*/
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static void __init rcu_bootup_announce_oddness(void)
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{
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if (IS_ENABLED(CONFIG_RCU_TRACE))
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pr_info("\tRCU event tracing is enabled.\n");
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if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||
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(!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))
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pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
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RCU_FANOUT);
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if (rcu_fanout_exact)
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pr_info("\tHierarchical RCU autobalancing is disabled.\n");
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if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ))
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pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
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if (IS_ENABLED(CONFIG_PROVE_RCU))
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pr_info("\tRCU lockdep checking is enabled.\n");
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if (RCU_NUM_LVLS >= 4)
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pr_info("\tFour(or more)-level hierarchy is enabled.\n");
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if (RCU_FANOUT_LEAF != 16)
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pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
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RCU_FANOUT_LEAF);
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if (rcu_fanout_leaf != RCU_FANOUT_LEAF)
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pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
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if (nr_cpu_ids != NR_CPUS)
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pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
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#ifdef CONFIG_RCU_BOOST
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pr_info("\tRCU priority boosting: priority %d delay %d ms.\n", kthread_prio, CONFIG_RCU_BOOST_DELAY);
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#endif
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if (blimit != DEFAULT_RCU_BLIMIT)
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pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit);
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if (qhimark != DEFAULT_RCU_QHIMARK)
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pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark);
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if (qlowmark != DEFAULT_RCU_QLOMARK)
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pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark);
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if (jiffies_till_first_fqs != ULONG_MAX)
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pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs);
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if (jiffies_till_next_fqs != ULONG_MAX)
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pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs);
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if (rcu_kick_kthreads)
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pr_info("\tKick kthreads if too-long grace period.\n");
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if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD))
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pr_info("\tRCU callback double-/use-after-free debug enabled.\n");
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if (gp_preinit_delay)
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pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay);
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if (gp_init_delay)
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pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay);
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if (gp_cleanup_delay)
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pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay);
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if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))
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pr_info("\tRCU debug extended QS entry/exit.\n");
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rcupdate_announce_bootup_oddness();
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}
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#ifdef CONFIG_PREEMPT_RCU
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RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
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static struct rcu_state *const rcu_state_p = &rcu_preempt_state;
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static struct rcu_data __percpu *const rcu_data_p = &rcu_preempt_data;
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static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
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bool wake);
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/*
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* Tell them what RCU they are running.
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*/
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static void __init rcu_bootup_announce(void)
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{
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pr_info("Preemptible hierarchical RCU implementation.\n");
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rcu_bootup_announce_oddness();
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}
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/* Flags for rcu_preempt_ctxt_queue() decision table. */
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#define RCU_GP_TASKS 0x8
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#define RCU_EXP_TASKS 0x4
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#define RCU_GP_BLKD 0x2
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#define RCU_EXP_BLKD 0x1
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/*
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* Queues a task preempted within an RCU-preempt read-side critical
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* section into the appropriate location within the ->blkd_tasks list,
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* depending on the states of any ongoing normal and expedited grace
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* periods. The ->gp_tasks pointer indicates which element the normal
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* grace period is waiting on (NULL if none), and the ->exp_tasks pointer
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* indicates which element the expedited grace period is waiting on (again,
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* NULL if none). If a grace period is waiting on a given element in the
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* ->blkd_tasks list, it also waits on all subsequent elements. Thus,
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* adding a task to the tail of the list blocks any grace period that is
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* already waiting on one of the elements. In contrast, adding a task
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* to the head of the list won't block any grace period that is already
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* waiting on one of the elements.
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*
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* This queuing is imprecise, and can sometimes make an ongoing grace
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* period wait for a task that is not strictly speaking blocking it.
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* Given the choice, we needlessly block a normal grace period rather than
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* blocking an expedited grace period.
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*
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* Note that an endless sequence of expedited grace periods still cannot
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* indefinitely postpone a normal grace period. Eventually, all of the
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* fixed number of preempted tasks blocking the normal grace period that are
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* not also blocking the expedited grace period will resume and complete
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* their RCU read-side critical sections. At that point, the ->gp_tasks
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* pointer will equal the ->exp_tasks pointer, at which point the end of
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* the corresponding expedited grace period will also be the end of the
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* normal grace period.
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*/
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static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
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__releases(rnp->lock) /* But leaves rrupts disabled. */
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{
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int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) +
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(rnp->exp_tasks ? RCU_EXP_TASKS : 0) +
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(rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) +
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(rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0);
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struct task_struct *t = current;
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lockdep_assert_held(&rnp->lock);
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/*
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* Decide where to queue the newly blocked task. In theory,
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* this could be an if-statement. In practice, when I tried
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* that, it was quite messy.
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*/
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switch (blkd_state) {
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case 0:
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case RCU_EXP_TASKS:
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case RCU_EXP_TASKS + RCU_GP_BLKD:
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case RCU_GP_TASKS:
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case RCU_GP_TASKS + RCU_EXP_TASKS:
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/*
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* Blocking neither GP, or first task blocking the normal
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* GP but not blocking the already-waiting expedited GP.
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* Queue at the head of the list to avoid unnecessarily
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* blocking the already-waiting GPs.
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*/
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list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
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break;
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case RCU_EXP_BLKD:
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case RCU_GP_BLKD:
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case RCU_GP_BLKD + RCU_EXP_BLKD:
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case RCU_GP_TASKS + RCU_EXP_BLKD:
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case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
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case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
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/*
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* First task arriving that blocks either GP, or first task
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* arriving that blocks the expedited GP (with the normal
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* GP already waiting), or a task arriving that blocks
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* both GPs with both GPs already waiting. Queue at the
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* tail of the list to avoid any GP waiting on any of the
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* already queued tasks that are not blocking it.
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*/
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list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);
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break;
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case RCU_EXP_TASKS + RCU_EXP_BLKD:
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case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
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case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD:
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/*
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* Second or subsequent task blocking the expedited GP.
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* The task either does not block the normal GP, or is the
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* first task blocking the normal GP. Queue just after
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* the first task blocking the expedited GP.
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*/
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list_add(&t->rcu_node_entry, rnp->exp_tasks);
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break;
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case RCU_GP_TASKS + RCU_GP_BLKD:
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case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD:
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/*
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* Second or subsequent task blocking the normal GP.
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* The task does not block the expedited GP. Queue just
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* after the first task blocking the normal GP.
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*/
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list_add(&t->rcu_node_entry, rnp->gp_tasks);
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break;
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default:
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/* Yet another exercise in excessive paranoia. */
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WARN_ON_ONCE(1);
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break;
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}
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/*
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* We have now queued the task. If it was the first one to
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* block either grace period, update the ->gp_tasks and/or
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* ->exp_tasks pointers, respectively, to reference the newly
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* blocked tasks.
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*/
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if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD))
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rnp->gp_tasks = &t->rcu_node_entry;
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if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
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rnp->exp_tasks = &t->rcu_node_entry;
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raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */
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/*
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* Report the quiescent state for the expedited GP. This expedited
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* GP should not be able to end until we report, so there should be
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* no need to check for a subsequent expedited GP. (Though we are
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* still in a quiescent state in any case.)
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*/
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if (blkd_state & RCU_EXP_BLKD &&
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t->rcu_read_unlock_special.b.exp_need_qs) {
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t->rcu_read_unlock_special.b.exp_need_qs = false;
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rcu_report_exp_rdp(rdp->rsp, rdp, true);
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} else {
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WARN_ON_ONCE(t->rcu_read_unlock_special.b.exp_need_qs);
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}
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}
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/*
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* Record a preemptible-RCU quiescent state for the specified CPU. Note
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* that this just means that the task currently running on the CPU is
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* not in a quiescent state. There might be any number of tasks blocked
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* while in an RCU read-side critical section.
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*
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* As with the other rcu_*_qs() functions, callers to this function
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* must disable preemption.
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*/
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static void rcu_preempt_qs(void)
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{
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RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_qs() invoked with preemption enabled!!!\n");
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if (__this_cpu_read(rcu_data_p->cpu_no_qs.s)) {
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trace_rcu_grace_period(TPS("rcu_preempt"),
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__this_cpu_read(rcu_data_p->gpnum),
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TPS("cpuqs"));
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__this_cpu_write(rcu_data_p->cpu_no_qs.b.norm, false);
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barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
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current->rcu_read_unlock_special.b.need_qs = false;
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}
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}
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/*
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* We have entered the scheduler, and the current task might soon be
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* context-switched away from. If this task is in an RCU read-side
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* critical section, we will no longer be able to rely on the CPU to
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* record that fact, so we enqueue the task on the blkd_tasks list.
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* The task will dequeue itself when it exits the outermost enclosing
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* RCU read-side critical section. Therefore, the current grace period
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* cannot be permitted to complete until the blkd_tasks list entries
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* predating the current grace period drain, in other words, until
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* rnp->gp_tasks becomes NULL.
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*
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* Caller must disable interrupts.
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*/
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static void rcu_preempt_note_context_switch(bool preempt)
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{
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struct task_struct *t = current;
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struct rcu_data *rdp;
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struct rcu_node *rnp;
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RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_preempt_note_context_switch() invoked with interrupts enabled!!!\n");
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WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0);
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if (t->rcu_read_lock_nesting > 0 &&
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!t->rcu_read_unlock_special.b.blocked) {
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/* Possibly blocking in an RCU read-side critical section. */
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rdp = this_cpu_ptr(rcu_state_p->rda);
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rnp = rdp->mynode;
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raw_spin_lock_rcu_node(rnp);
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t->rcu_read_unlock_special.b.blocked = true;
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t->rcu_blocked_node = rnp;
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/*
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* Verify the CPU's sanity, trace the preemption, and
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* then queue the task as required based on the states
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* of any ongoing and expedited grace periods.
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*/
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WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);
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WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
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trace_rcu_preempt_task(rdp->rsp->name,
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t->pid,
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(rnp->qsmask & rdp->grpmask)
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? rnp->gpnum
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: rnp->gpnum + 1);
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rcu_preempt_ctxt_queue(rnp, rdp);
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} else if (t->rcu_read_lock_nesting < 0 &&
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t->rcu_read_unlock_special.s) {
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/*
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* Complete exit from RCU read-side critical section on
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* behalf of preempted instance of __rcu_read_unlock().
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*/
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rcu_read_unlock_special(t);
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}
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/*
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* Either we were not in an RCU read-side critical section to
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* begin with, or we have now recorded that critical section
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* globally. Either way, we can now note a quiescent state
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* for this CPU. Again, if we were in an RCU read-side critical
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* section, and if that critical section was blocking the current
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* grace period, then the fact that the task has been enqueued
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* means that we continue to block the current grace period.
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*/
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rcu_preempt_qs();
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}
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/*
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* Check for preempted RCU readers blocking the current grace period
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* for the specified rcu_node structure. If the caller needs a reliable
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* answer, it must hold the rcu_node's ->lock.
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*/
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static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
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{
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return rnp->gp_tasks != NULL;
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}
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/*
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* Advance a ->blkd_tasks-list pointer to the next entry, instead
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* returning NULL if at the end of the list.
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*/
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static struct list_head *rcu_next_node_entry(struct task_struct *t,
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struct rcu_node *rnp)
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{
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struct list_head *np;
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np = t->rcu_node_entry.next;
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if (np == &rnp->blkd_tasks)
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np = NULL;
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return np;
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}
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/*
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* Return true if the specified rcu_node structure has tasks that were
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* preempted within an RCU read-side critical section.
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*/
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static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
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{
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return !list_empty(&rnp->blkd_tasks);
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}
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/*
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* Handle special cases during rcu_read_unlock(), such as needing to
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* notify RCU core processing or task having blocked during the RCU
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* read-side critical section.
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*/
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void rcu_read_unlock_special(struct task_struct *t)
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{
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bool empty_exp;
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bool empty_norm;
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bool empty_exp_now;
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unsigned long flags;
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struct list_head *np;
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bool drop_boost_mutex = false;
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struct rcu_data *rdp;
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struct rcu_node *rnp;
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union rcu_special special;
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/* NMI handlers cannot block and cannot safely manipulate state. */
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if (in_nmi())
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return;
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local_irq_save(flags);
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/*
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* If RCU core is waiting for this CPU to exit its critical section,
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* report the fact that it has exited. Because irqs are disabled,
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* t->rcu_read_unlock_special cannot change.
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*/
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special = t->rcu_read_unlock_special;
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if (special.b.need_qs) {
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|
rcu_preempt_qs();
|
|
t->rcu_read_unlock_special.b.need_qs = false;
|
|
if (!t->rcu_read_unlock_special.s) {
|
|
local_irq_restore(flags);
|
|
return;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Respond to a request for an expedited grace period, but only if
|
|
* we were not preempted, meaning that we were running on the same
|
|
* CPU throughout. If we were preempted, the exp_need_qs flag
|
|
* would have been cleared at the time of the first preemption,
|
|
* and the quiescent state would be reported when we were dequeued.
|
|
*/
|
|
if (special.b.exp_need_qs) {
|
|
WARN_ON_ONCE(special.b.blocked);
|
|
t->rcu_read_unlock_special.b.exp_need_qs = false;
|
|
rdp = this_cpu_ptr(rcu_state_p->rda);
|
|
rcu_report_exp_rdp(rcu_state_p, rdp, true);
|
|
if (!t->rcu_read_unlock_special.s) {
|
|
local_irq_restore(flags);
|
|
return;
|
|
}
|
|
}
|
|
|
|
/* Hardware IRQ handlers cannot block, complain if they get here. */
|
|
if (in_irq() || in_serving_softirq()) {
|
|
lockdep_rcu_suspicious(__FILE__, __LINE__,
|
|
"rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n");
|
|
pr_alert("->rcu_read_unlock_special: %#x (b: %d, enq: %d nq: %d)\n",
|
|
t->rcu_read_unlock_special.s,
|
|
t->rcu_read_unlock_special.b.blocked,
|
|
t->rcu_read_unlock_special.b.exp_need_qs,
|
|
t->rcu_read_unlock_special.b.need_qs);
|
|
local_irq_restore(flags);
|
|
return;
|
|
}
|
|
|
|
/* Clean up if blocked during RCU read-side critical section. */
|
|
if (special.b.blocked) {
|
|
t->rcu_read_unlock_special.b.blocked = false;
|
|
|
|
/*
|
|
* Remove this task from the list it blocked on. The task
|
|
* now remains queued on the rcu_node corresponding to the
|
|
* CPU it first blocked on, so there is no longer any need
|
|
* to loop. Retain a WARN_ON_ONCE() out of sheer paranoia.
|
|
*/
|
|
rnp = t->rcu_blocked_node;
|
|
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
|
|
WARN_ON_ONCE(rnp != t->rcu_blocked_node);
|
|
empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
|
|
empty_exp = sync_rcu_preempt_exp_done(rnp);
|
|
smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
|
|
np = rcu_next_node_entry(t, rnp);
|
|
list_del_init(&t->rcu_node_entry);
|
|
t->rcu_blocked_node = NULL;
|
|
trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
|
|
rnp->gpnum, t->pid);
|
|
if (&t->rcu_node_entry == rnp->gp_tasks)
|
|
rnp->gp_tasks = np;
|
|
if (&t->rcu_node_entry == rnp->exp_tasks)
|
|
rnp->exp_tasks = np;
|
|
if (IS_ENABLED(CONFIG_RCU_BOOST)) {
|
|
if (&t->rcu_node_entry == rnp->boost_tasks)
|
|
rnp->boost_tasks = np;
|
|
/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
|
|
drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
|
|
}
|
|
|
|
/*
|
|
* If this was the last task on the current list, and if
|
|
* we aren't waiting on any CPUs, report the quiescent state.
|
|
* Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
|
|
* so we must take a snapshot of the expedited state.
|
|
*/
|
|
empty_exp_now = sync_rcu_preempt_exp_done(rnp);
|
|
if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
|
|
trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
|
|
rnp->gpnum,
|
|
0, rnp->qsmask,
|
|
rnp->level,
|
|
rnp->grplo,
|
|
rnp->grphi,
|
|
!!rnp->gp_tasks);
|
|
rcu_report_unblock_qs_rnp(rcu_state_p, rnp, flags);
|
|
} else {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
}
|
|
|
|
/* Unboost if we were boosted. */
|
|
if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
|
|
rt_mutex_unlock(&rnp->boost_mtx);
|
|
|
|
/*
|
|
* If this was the last task on the expedited lists,
|
|
* then we need to report up the rcu_node hierarchy.
|
|
*/
|
|
if (!empty_exp && empty_exp_now)
|
|
rcu_report_exp_rnp(rcu_state_p, rnp, true);
|
|
} else {
|
|
local_irq_restore(flags);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Dump detailed information for all tasks blocking the current RCU
|
|
* grace period on the specified rcu_node structure.
|
|
*/
|
|
static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
|
|
{
|
|
unsigned long flags;
|
|
struct task_struct *t;
|
|
|
|
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
|
if (!rcu_preempt_blocked_readers_cgp(rnp)) {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
return;
|
|
}
|
|
t = list_entry(rnp->gp_tasks->prev,
|
|
struct task_struct, rcu_node_entry);
|
|
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
|
|
sched_show_task(t);
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
}
|
|
|
|
/*
|
|
* Dump detailed information for all tasks blocking the current RCU
|
|
* grace period.
|
|
*/
|
|
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
|
|
{
|
|
struct rcu_node *rnp = rcu_get_root(rsp);
|
|
|
|
rcu_print_detail_task_stall_rnp(rnp);
|
|
rcu_for_each_leaf_node(rsp, rnp)
|
|
rcu_print_detail_task_stall_rnp(rnp);
|
|
}
|
|
|
|
static void rcu_print_task_stall_begin(struct rcu_node *rnp)
|
|
{
|
|
pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
|
|
rnp->level, rnp->grplo, rnp->grphi);
|
|
}
|
|
|
|
static void rcu_print_task_stall_end(void)
|
|
{
|
|
pr_cont("\n");
|
|
}
|
|
|
|
/*
|
|
* Scan the current list of tasks blocked within RCU read-side critical
|
|
* sections, printing out the tid of each.
|
|
*/
|
|
static int rcu_print_task_stall(struct rcu_node *rnp)
|
|
{
|
|
struct task_struct *t;
|
|
int ndetected = 0;
|
|
|
|
if (!rcu_preempt_blocked_readers_cgp(rnp))
|
|
return 0;
|
|
rcu_print_task_stall_begin(rnp);
|
|
t = list_entry(rnp->gp_tasks->prev,
|
|
struct task_struct, rcu_node_entry);
|
|
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
|
|
pr_cont(" P%d", t->pid);
|
|
ndetected++;
|
|
}
|
|
rcu_print_task_stall_end();
|
|
return ndetected;
|
|
}
|
|
|
|
/*
|
|
* Scan the current list of tasks blocked within RCU read-side critical
|
|
* sections, printing out the tid of each that is blocking the current
|
|
* expedited grace period.
|
|
*/
|
|
static int rcu_print_task_exp_stall(struct rcu_node *rnp)
|
|
{
|
|
struct task_struct *t;
|
|
int ndetected = 0;
|
|
|
|
if (!rnp->exp_tasks)
|
|
return 0;
|
|
t = list_entry(rnp->exp_tasks->prev,
|
|
struct task_struct, rcu_node_entry);
|
|
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
|
|
pr_cont(" P%d", t->pid);
|
|
ndetected++;
|
|
}
|
|
return ndetected;
|
|
}
|
|
|
|
/*
|
|
* Check that the list of blocked tasks for the newly completed grace
|
|
* period is in fact empty. It is a serious bug to complete a grace
|
|
* period that still has RCU readers blocked! This function must be
|
|
* invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
|
|
* must be held by the caller.
|
|
*
|
|
* Also, if there are blocked tasks on the list, they automatically
|
|
* block the newly created grace period, so set up ->gp_tasks accordingly.
|
|
*/
|
|
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
|
|
{
|
|
RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
|
|
WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
|
|
if (rcu_preempt_has_tasks(rnp))
|
|
rnp->gp_tasks = rnp->blkd_tasks.next;
|
|
WARN_ON_ONCE(rnp->qsmask);
|
|
}
|
|
|
|
/*
|
|
* Check for a quiescent state from the current CPU. When a task blocks,
|
|
* the task is recorded in the corresponding CPU's rcu_node structure,
|
|
* which is checked elsewhere.
|
|
*
|
|
* Caller must disable hard irqs.
|
|
*/
|
|
static void rcu_preempt_check_callbacks(void)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
if (t->rcu_read_lock_nesting == 0) {
|
|
rcu_preempt_qs();
|
|
return;
|
|
}
|
|
if (t->rcu_read_lock_nesting > 0 &&
|
|
__this_cpu_read(rcu_data_p->core_needs_qs) &&
|
|
__this_cpu_read(rcu_data_p->cpu_no_qs.b.norm))
|
|
t->rcu_read_unlock_special.b.need_qs = true;
|
|
}
|
|
|
|
#ifdef CONFIG_RCU_BOOST
|
|
|
|
static void rcu_preempt_do_callbacks(void)
|
|
{
|
|
rcu_do_batch(rcu_state_p, this_cpu_ptr(rcu_data_p));
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_RCU_BOOST */
|
|
|
|
/**
|
|
* call_rcu() - Queue an RCU callback for invocation after a grace period.
|
|
* @head: structure to be used for queueing the RCU updates.
|
|
* @func: actual callback function to be invoked after the grace period
|
|
*
|
|
* The callback function will be invoked some time after a full grace
|
|
* period elapses, in other words after all pre-existing RCU read-side
|
|
* critical sections have completed. However, the callback function
|
|
* might well execute concurrently with RCU read-side critical sections
|
|
* that started after call_rcu() was invoked. RCU read-side critical
|
|
* sections are delimited by rcu_read_lock() and rcu_read_unlock(),
|
|
* and may be nested.
|
|
*
|
|
* Note that all CPUs must agree that the grace period extended beyond
|
|
* all pre-existing RCU read-side critical section. On systems with more
|
|
* than one CPU, this means that when "func()" is invoked, each CPU is
|
|
* guaranteed to have executed a full memory barrier since the end of its
|
|
* last RCU read-side critical section whose beginning preceded the call
|
|
* to call_rcu(). It also means that each CPU executing an RCU read-side
|
|
* critical section that continues beyond the start of "func()" must have
|
|
* executed a memory barrier after the call_rcu() but before the beginning
|
|
* of that RCU read-side critical section. Note that these guarantees
|
|
* include CPUs that are offline, idle, or executing in user mode, as
|
|
* well as CPUs that are executing in the kernel.
|
|
*
|
|
* Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
|
|
* resulting RCU callback function "func()", then both CPU A and CPU B are
|
|
* guaranteed to execute a full memory barrier during the time interval
|
|
* between the call to call_rcu() and the invocation of "func()" -- even
|
|
* if CPU A and CPU B are the same CPU (but again only if the system has
|
|
* more than one CPU).
|
|
*/
|
|
void call_rcu(struct rcu_head *head, rcu_callback_t func)
|
|
{
|
|
__call_rcu(head, func, rcu_state_p, -1, 0);
|
|
}
|
|
EXPORT_SYMBOL_GPL(call_rcu);
|
|
|
|
/**
|
|
* synchronize_rcu - wait until a grace period has elapsed.
|
|
*
|
|
* Control will return to the caller some time after a full grace
|
|
* period has elapsed, in other words after all currently executing RCU
|
|
* read-side critical sections have completed. Note, however, that
|
|
* upon return from synchronize_rcu(), the caller might well be executing
|
|
* concurrently with new RCU read-side critical sections that began while
|
|
* synchronize_rcu() was waiting. RCU read-side critical sections are
|
|
* delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
|
|
*
|
|
* See the description of synchronize_sched() for more detailed
|
|
* information on memory-ordering guarantees. However, please note
|
|
* that -only- the memory-ordering guarantees apply. For example,
|
|
* synchronize_rcu() is -not- guaranteed to wait on things like code
|
|
* protected by preempt_disable(), instead, synchronize_rcu() is -only-
|
|
* guaranteed to wait on RCU read-side critical sections, that is, sections
|
|
* of code protected by rcu_read_lock().
|
|
*/
|
|
void synchronize_rcu(void)
|
|
{
|
|
RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
|
|
lock_is_held(&rcu_lock_map) ||
|
|
lock_is_held(&rcu_sched_lock_map),
|
|
"Illegal synchronize_rcu() in RCU read-side critical section");
|
|
if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
|
|
return;
|
|
if (rcu_gp_is_expedited())
|
|
synchronize_rcu_expedited();
|
|
else
|
|
wait_rcu_gp(call_rcu);
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_rcu);
|
|
|
|
/**
|
|
* rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
|
|
*
|
|
* Note that this primitive does not necessarily wait for an RCU grace period
|
|
* to complete. For example, if there are no RCU callbacks queued anywhere
|
|
* in the system, then rcu_barrier() is within its rights to return
|
|
* immediately, without waiting for anything, much less an RCU grace period.
|
|
*/
|
|
void rcu_barrier(void)
|
|
{
|
|
_rcu_barrier(rcu_state_p);
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_barrier);
|
|
|
|
/*
|
|
* Initialize preemptible RCU's state structures.
|
|
*/
|
|
static void __init __rcu_init_preempt(void)
|
|
{
|
|
rcu_init_one(rcu_state_p);
|
|
}
|
|
|
|
/*
|
|
* Check for a task exiting while in a preemptible-RCU read-side
|
|
* critical section, clean up if so. No need to issue warnings,
|
|
* as debug_check_no_locks_held() already does this if lockdep
|
|
* is enabled.
|
|
*/
|
|
void exit_rcu(void)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
if (likely(list_empty(¤t->rcu_node_entry)))
|
|
return;
|
|
t->rcu_read_lock_nesting = 1;
|
|
barrier();
|
|
t->rcu_read_unlock_special.b.blocked = true;
|
|
__rcu_read_unlock();
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_PREEMPT_RCU */
|
|
|
|
static struct rcu_state *const rcu_state_p = &rcu_sched_state;
|
|
|
|
/*
|
|
* Tell them what RCU they are running.
|
|
*/
|
|
static void __init rcu_bootup_announce(void)
|
|
{
|
|
pr_info("Hierarchical RCU implementation.\n");
|
|
rcu_bootup_announce_oddness();
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* CPUs being in quiescent states.
|
|
*/
|
|
static void rcu_preempt_note_context_switch(bool preempt)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, there are never any preempted
|
|
* RCU readers.
|
|
*/
|
|
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Because there is no preemptible RCU, there can be no readers blocked.
|
|
*/
|
|
static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* tasks blocked within RCU read-side critical sections.
|
|
*/
|
|
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* tasks blocked within RCU read-side critical sections.
|
|
*/
|
|
static int rcu_print_task_stall(struct rcu_node *rnp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* tasks blocked within RCU read-side critical sections that are
|
|
* blocking the current expedited grace period.
|
|
*/
|
|
static int rcu_print_task_exp_stall(struct rcu_node *rnp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Because there is no preemptible RCU, there can be no readers blocked,
|
|
* so there is no need to check for blocked tasks. So check only for
|
|
* bogus qsmask values.
|
|
*/
|
|
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
|
|
{
|
|
WARN_ON_ONCE(rnp->qsmask);
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it never has any callbacks
|
|
* to check.
|
|
*/
|
|
static void rcu_preempt_check_callbacks(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, rcu_barrier() is just
|
|
* another name for rcu_barrier_sched().
|
|
*/
|
|
void rcu_barrier(void)
|
|
{
|
|
rcu_barrier_sched();
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_barrier);
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it need not be initialized.
|
|
*/
|
|
static void __init __rcu_init_preempt(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, tasks cannot possibly exit
|
|
* while in preemptible RCU read-side critical sections.
|
|
*/
|
|
void exit_rcu(void)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
|
|
|
|
#ifdef CONFIG_RCU_BOOST
|
|
|
|
#include "../locking/rtmutex_common.h"
|
|
|
|
static void rcu_wake_cond(struct task_struct *t, int status)
|
|
{
|
|
/*
|
|
* If the thread is yielding, only wake it when this
|
|
* is invoked from idle
|
|
*/
|
|
if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
|
|
wake_up_process(t);
|
|
}
|
|
|
|
/*
|
|
* Carry out RCU priority boosting on the task indicated by ->exp_tasks
|
|
* or ->boost_tasks, advancing the pointer to the next task in the
|
|
* ->blkd_tasks list.
|
|
*
|
|
* Note that irqs must be enabled: boosting the task can block.
|
|
* Returns 1 if there are more tasks needing to be boosted.
|
|
*/
|
|
static int rcu_boost(struct rcu_node *rnp)
|
|
{
|
|
unsigned long flags;
|
|
struct task_struct *t;
|
|
struct list_head *tb;
|
|
|
|
if (READ_ONCE(rnp->exp_tasks) == NULL &&
|
|
READ_ONCE(rnp->boost_tasks) == NULL)
|
|
return 0; /* Nothing left to boost. */
|
|
|
|
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
|
|
|
/*
|
|
* Recheck under the lock: all tasks in need of boosting
|
|
* might exit their RCU read-side critical sections on their own.
|
|
*/
|
|
if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Preferentially boost tasks blocking expedited grace periods.
|
|
* This cannot starve the normal grace periods because a second
|
|
* expedited grace period must boost all blocked tasks, including
|
|
* those blocking the pre-existing normal grace period.
|
|
*/
|
|
if (rnp->exp_tasks != NULL) {
|
|
tb = rnp->exp_tasks;
|
|
rnp->n_exp_boosts++;
|
|
} else {
|
|
tb = rnp->boost_tasks;
|
|
rnp->n_normal_boosts++;
|
|
}
|
|
rnp->n_tasks_boosted++;
|
|
|
|
/*
|
|
* We boost task t by manufacturing an rt_mutex that appears to
|
|
* be held by task t. We leave a pointer to that rt_mutex where
|
|
* task t can find it, and task t will release the mutex when it
|
|
* exits its outermost RCU read-side critical section. Then
|
|
* simply acquiring this artificial rt_mutex will boost task
|
|
* t's priority. (Thanks to tglx for suggesting this approach!)
|
|
*
|
|
* Note that task t must acquire rnp->lock to remove itself from
|
|
* the ->blkd_tasks list, which it will do from exit() if from
|
|
* nowhere else. We therefore are guaranteed that task t will
|
|
* stay around at least until we drop rnp->lock. Note that
|
|
* rnp->lock also resolves races between our priority boosting
|
|
* and task t's exiting its outermost RCU read-side critical
|
|
* section.
|
|
*/
|
|
t = container_of(tb, struct task_struct, rcu_node_entry);
|
|
rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
/* Lock only for side effect: boosts task t's priority. */
|
|
rt_mutex_lock(&rnp->boost_mtx);
|
|
rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
|
|
|
|
return READ_ONCE(rnp->exp_tasks) != NULL ||
|
|
READ_ONCE(rnp->boost_tasks) != NULL;
|
|
}
|
|
|
|
/*
|
|
* Priority-boosting kthread, one per leaf rcu_node.
|
|
*/
|
|
static int rcu_boost_kthread(void *arg)
|
|
{
|
|
struct rcu_node *rnp = (struct rcu_node *)arg;
|
|
int spincnt = 0;
|
|
int more2boost;
|
|
|
|
trace_rcu_utilization(TPS("Start boost kthread@init"));
|
|
for (;;) {
|
|
rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
|
|
trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
|
|
rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
|
|
trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
|
|
rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
|
|
more2boost = rcu_boost(rnp);
|
|
if (more2boost)
|
|
spincnt++;
|
|
else
|
|
spincnt = 0;
|
|
if (spincnt > 10) {
|
|
rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
|
|
trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
|
|
schedule_timeout_interruptible(2);
|
|
trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
|
|
spincnt = 0;
|
|
}
|
|
}
|
|
/* NOTREACHED */
|
|
trace_rcu_utilization(TPS("End boost kthread@notreached"));
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Check to see if it is time to start boosting RCU readers that are
|
|
* blocking the current grace period, and, if so, tell the per-rcu_node
|
|
* kthread to start boosting them. If there is an expedited grace
|
|
* period in progress, it is always time to boost.
|
|
*
|
|
* The caller must hold rnp->lock, which this function releases.
|
|
* The ->boost_kthread_task is immortal, so we don't need to worry
|
|
* about it going away.
|
|
*/
|
|
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
|
|
__releases(rnp->lock)
|
|
{
|
|
struct task_struct *t;
|
|
|
|
lockdep_assert_held(&rnp->lock);
|
|
if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
return;
|
|
}
|
|
if (rnp->exp_tasks != NULL ||
|
|
(rnp->gp_tasks != NULL &&
|
|
rnp->boost_tasks == NULL &&
|
|
rnp->qsmask == 0 &&
|
|
ULONG_CMP_GE(jiffies, rnp->boost_time))) {
|
|
if (rnp->exp_tasks == NULL)
|
|
rnp->boost_tasks = rnp->gp_tasks;
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
t = rnp->boost_kthread_task;
|
|
if (t)
|
|
rcu_wake_cond(t, rnp->boost_kthread_status);
|
|
} else {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Wake up the per-CPU kthread to invoke RCU callbacks.
|
|
*/
|
|
static void invoke_rcu_callbacks_kthread(void)
|
|
{
|
|
unsigned long flags;
|
|
|
|
local_irq_save(flags);
|
|
__this_cpu_write(rcu_cpu_has_work, 1);
|
|
if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
|
|
current != __this_cpu_read(rcu_cpu_kthread_task)) {
|
|
rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
|
|
__this_cpu_read(rcu_cpu_kthread_status));
|
|
}
|
|
local_irq_restore(flags);
|
|
}
|
|
|
|
/*
|
|
* Is the current CPU running the RCU-callbacks kthread?
|
|
* Caller must have preemption disabled.
|
|
*/
|
|
static bool rcu_is_callbacks_kthread(void)
|
|
{
|
|
return __this_cpu_read(rcu_cpu_kthread_task) == current;
|
|
}
|
|
|
|
#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
|
|
|
|
/*
|
|
* Do priority-boost accounting for the start of a new grace period.
|
|
*/
|
|
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
|
|
{
|
|
rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
|
|
}
|
|
|
|
/*
|
|
* Create an RCU-boost kthread for the specified node if one does not
|
|
* already exist. We only create this kthread for preemptible RCU.
|
|
* Returns zero if all is well, a negated errno otherwise.
|
|
*/
|
|
static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
|
|
struct rcu_node *rnp)
|
|
{
|
|
int rnp_index = rnp - &rsp->node[0];
|
|
unsigned long flags;
|
|
struct sched_param sp;
|
|
struct task_struct *t;
|
|
|
|
if (rcu_state_p != rsp)
|
|
return 0;
|
|
|
|
if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
|
|
return 0;
|
|
|
|
rsp->boost = 1;
|
|
if (rnp->boost_kthread_task != NULL)
|
|
return 0;
|
|
t = kthread_create(rcu_boost_kthread, (void *)rnp,
|
|
"rcub/%d", rnp_index);
|
|
if (IS_ERR(t))
|
|
return PTR_ERR(t);
|
|
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
|
rnp->boost_kthread_task = t;
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
sp.sched_priority = kthread_prio;
|
|
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
|
|
wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
|
|
return 0;
|
|
}
|
|
|
|
static void rcu_kthread_do_work(void)
|
|
{
|
|
rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
|
|
rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
|
|
rcu_preempt_do_callbacks();
|
|
}
|
|
|
|
static void rcu_cpu_kthread_setup(unsigned int cpu)
|
|
{
|
|
struct sched_param sp;
|
|
|
|
sp.sched_priority = kthread_prio;
|
|
sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
|
|
}
|
|
|
|
static void rcu_cpu_kthread_park(unsigned int cpu)
|
|
{
|
|
per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
|
|
}
|
|
|
|
static int rcu_cpu_kthread_should_run(unsigned int cpu)
|
|
{
|
|
return __this_cpu_read(rcu_cpu_has_work);
|
|
}
|
|
|
|
/*
|
|
* Per-CPU kernel thread that invokes RCU callbacks. This replaces the
|
|
* RCU softirq used in flavors and configurations of RCU that do not
|
|
* support RCU priority boosting.
|
|
*/
|
|
static void rcu_cpu_kthread(unsigned int cpu)
|
|
{
|
|
unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
|
|
char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
|
|
int spincnt;
|
|
|
|
for (spincnt = 0; spincnt < 10; spincnt++) {
|
|
trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
|
|
local_bh_disable();
|
|
*statusp = RCU_KTHREAD_RUNNING;
|
|
this_cpu_inc(rcu_cpu_kthread_loops);
|
|
local_irq_disable();
|
|
work = *workp;
|
|
*workp = 0;
|
|
local_irq_enable();
|
|
if (work)
|
|
rcu_kthread_do_work();
|
|
local_bh_enable();
|
|
if (*workp == 0) {
|
|
trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
|
|
*statusp = RCU_KTHREAD_WAITING;
|
|
return;
|
|
}
|
|
}
|
|
*statusp = RCU_KTHREAD_YIELDING;
|
|
trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
|
|
schedule_timeout_interruptible(2);
|
|
trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
|
|
*statusp = RCU_KTHREAD_WAITING;
|
|
}
|
|
|
|
/*
|
|
* Set the per-rcu_node kthread's affinity to cover all CPUs that are
|
|
* served by the rcu_node in question. The CPU hotplug lock is still
|
|
* held, so the value of rnp->qsmaskinit will be stable.
|
|
*
|
|
* We don't include outgoingcpu in the affinity set, use -1 if there is
|
|
* no outgoing CPU. If there are no CPUs left in the affinity set,
|
|
* this function allows the kthread to execute on any CPU.
|
|
*/
|
|
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
|
|
{
|
|
struct task_struct *t = rnp->boost_kthread_task;
|
|
unsigned long mask = rcu_rnp_online_cpus(rnp);
|
|
cpumask_var_t cm;
|
|
int cpu;
|
|
|
|
if (!t)
|
|
return;
|
|
if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
|
|
return;
|
|
for_each_leaf_node_possible_cpu(rnp, cpu)
|
|
if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
|
|
cpu != outgoingcpu)
|
|
cpumask_set_cpu(cpu, cm);
|
|
if (cpumask_weight(cm) == 0)
|
|
cpumask_setall(cm);
|
|
set_cpus_allowed_ptr(t, cm);
|
|
free_cpumask_var(cm);
|
|
}
|
|
|
|
static struct smp_hotplug_thread rcu_cpu_thread_spec = {
|
|
.store = &rcu_cpu_kthread_task,
|
|
.thread_should_run = rcu_cpu_kthread_should_run,
|
|
.thread_fn = rcu_cpu_kthread,
|
|
.thread_comm = "rcuc/%u",
|
|
.setup = rcu_cpu_kthread_setup,
|
|
.park = rcu_cpu_kthread_park,
|
|
};
|
|
|
|
/*
|
|
* Spawn boost kthreads -- called as soon as the scheduler is running.
|
|
*/
|
|
static void __init rcu_spawn_boost_kthreads(void)
|
|
{
|
|
struct rcu_node *rnp;
|
|
int cpu;
|
|
|
|
for_each_possible_cpu(cpu)
|
|
per_cpu(rcu_cpu_has_work, cpu) = 0;
|
|
BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
|
|
rcu_for_each_leaf_node(rcu_state_p, rnp)
|
|
(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
|
|
}
|
|
|
|
static void rcu_prepare_kthreads(int cpu)
|
|
{
|
|
struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
|
|
struct rcu_node *rnp = rdp->mynode;
|
|
|
|
/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
|
|
if (rcu_scheduler_fully_active)
|
|
(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_BOOST */
|
|
|
|
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
|
|
__releases(rnp->lock)
|
|
{
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
}
|
|
|
|
static void invoke_rcu_callbacks_kthread(void)
|
|
{
|
|
WARN_ON_ONCE(1);
|
|
}
|
|
|
|
static bool rcu_is_callbacks_kthread(void)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
|
|
{
|
|
}
|
|
|
|
static void __init rcu_spawn_boost_kthreads(void)
|
|
{
|
|
}
|
|
|
|
static void rcu_prepare_kthreads(int cpu)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_BOOST */
|
|
|
|
#if !defined(CONFIG_RCU_FAST_NO_HZ)
|
|
|
|
/*
|
|
* Check to see if any future RCU-related work will need to be done
|
|
* by the current CPU, even if none need be done immediately, returning
|
|
* 1 if so. This function is part of the RCU implementation; it is -not-
|
|
* an exported member of the RCU API.
|
|
*
|
|
* Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
|
|
* any flavor of RCU.
|
|
*/
|
|
int rcu_needs_cpu(u64 basemono, u64 *nextevt)
|
|
{
|
|
*nextevt = KTIME_MAX;
|
|
return rcu_cpu_has_callbacks(NULL);
|
|
}
|
|
|
|
/*
|
|
* Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
|
|
* after it.
|
|
*/
|
|
static void rcu_cleanup_after_idle(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
|
|
* is nothing.
|
|
*/
|
|
static void rcu_prepare_for_idle(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Don't bother keeping a running count of the number of RCU callbacks
|
|
* posted because CONFIG_RCU_FAST_NO_HZ=n.
|
|
*/
|
|
static void rcu_idle_count_callbacks_posted(void)
|
|
{
|
|
}
|
|
|
|
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
|
|
|
|
/*
|
|
* This code is invoked when a CPU goes idle, at which point we want
|
|
* to have the CPU do everything required for RCU so that it can enter
|
|
* the energy-efficient dyntick-idle mode. This is handled by a
|
|
* state machine implemented by rcu_prepare_for_idle() below.
|
|
*
|
|
* The following three proprocessor symbols control this state machine:
|
|
*
|
|
* RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
|
|
* to sleep in dyntick-idle mode with RCU callbacks pending. This
|
|
* is sized to be roughly one RCU grace period. Those energy-efficiency
|
|
* benchmarkers who might otherwise be tempted to set this to a large
|
|
* number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
|
|
* system. And if you are -that- concerned about energy efficiency,
|
|
* just power the system down and be done with it!
|
|
* RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
|
|
* permitted to sleep in dyntick-idle mode with only lazy RCU
|
|
* callbacks pending. Setting this too high can OOM your system.
|
|
*
|
|
* The values below work well in practice. If future workloads require
|
|
* adjustment, they can be converted into kernel config parameters, though
|
|
* making the state machine smarter might be a better option.
|
|
*/
|
|
#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
|
|
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
|
|
|
|
static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
|
|
module_param(rcu_idle_gp_delay, int, 0644);
|
|
static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
|
|
module_param(rcu_idle_lazy_gp_delay, int, 0644);
|
|
|
|
/*
|
|
* Try to advance callbacks for all flavors of RCU on the current CPU, but
|
|
* only if it has been awhile since the last time we did so. Afterwards,
|
|
* if there are any callbacks ready for immediate invocation, return true.
|
|
*/
|
|
static bool __maybe_unused rcu_try_advance_all_cbs(void)
|
|
{
|
|
bool cbs_ready = false;
|
|
struct rcu_data *rdp;
|
|
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
|
|
struct rcu_node *rnp;
|
|
struct rcu_state *rsp;
|
|
|
|
/* Exit early if we advanced recently. */
|
|
if (jiffies == rdtp->last_advance_all)
|
|
return false;
|
|
rdtp->last_advance_all = jiffies;
|
|
|
|
for_each_rcu_flavor(rsp) {
|
|
rdp = this_cpu_ptr(rsp->rda);
|
|
rnp = rdp->mynode;
|
|
|
|
/*
|
|
* Don't bother checking unless a grace period has
|
|
* completed since we last checked and there are
|
|
* callbacks not yet ready to invoke.
|
|
*/
|
|
if ((rdp->completed != rnp->completed ||
|
|
unlikely(READ_ONCE(rdp->gpwrap))) &&
|
|
rcu_segcblist_pend_cbs(&rdp->cblist))
|
|
note_gp_changes(rsp, rdp);
|
|
|
|
if (rcu_segcblist_ready_cbs(&rdp->cblist))
|
|
cbs_ready = true;
|
|
}
|
|
return cbs_ready;
|
|
}
|
|
|
|
/*
|
|
* Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
|
|
* to invoke. If the CPU has callbacks, try to advance them. Tell the
|
|
* caller to set the timeout based on whether or not there are non-lazy
|
|
* callbacks.
|
|
*
|
|
* The caller must have disabled interrupts.
|
|
*/
|
|
int rcu_needs_cpu(u64 basemono, u64 *nextevt)
|
|
{
|
|
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
|
|
unsigned long dj;
|
|
|
|
RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_needs_cpu() invoked with irqs enabled!!!");
|
|
|
|
/* Snapshot to detect later posting of non-lazy callback. */
|
|
rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
|
|
|
|
/* If no callbacks, RCU doesn't need the CPU. */
|
|
if (!rcu_cpu_has_callbacks(&rdtp->all_lazy)) {
|
|
*nextevt = KTIME_MAX;
|
|
return 0;
|
|
}
|
|
|
|
/* Attempt to advance callbacks. */
|
|
if (rcu_try_advance_all_cbs()) {
|
|
/* Some ready to invoke, so initiate later invocation. */
|
|
invoke_rcu_core();
|
|
return 1;
|
|
}
|
|
rdtp->last_accelerate = jiffies;
|
|
|
|
/* Request timer delay depending on laziness, and round. */
|
|
if (!rdtp->all_lazy) {
|
|
dj = round_up(rcu_idle_gp_delay + jiffies,
|
|
rcu_idle_gp_delay) - jiffies;
|
|
} else {
|
|
dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
|
|
}
|
|
*nextevt = basemono + dj * TICK_NSEC;
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Prepare a CPU for idle from an RCU perspective. The first major task
|
|
* is to sense whether nohz mode has been enabled or disabled via sysfs.
|
|
* The second major task is to check to see if a non-lazy callback has
|
|
* arrived at a CPU that previously had only lazy callbacks. The third
|
|
* major task is to accelerate (that is, assign grace-period numbers to)
|
|
* any recently arrived callbacks.
|
|
*
|
|
* The caller must have disabled interrupts.
|
|
*/
|
|
static void rcu_prepare_for_idle(void)
|
|
{
|
|
bool needwake;
|
|
struct rcu_data *rdp;
|
|
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
|
|
struct rcu_node *rnp;
|
|
struct rcu_state *rsp;
|
|
int tne;
|
|
|
|
RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_prepare_for_idle() invoked with irqs enabled!!!");
|
|
if (rcu_is_nocb_cpu(smp_processor_id()))
|
|
return;
|
|
|
|
/* Handle nohz enablement switches conservatively. */
|
|
tne = READ_ONCE(tick_nohz_active);
|
|
if (tne != rdtp->tick_nohz_enabled_snap) {
|
|
if (rcu_cpu_has_callbacks(NULL))
|
|
invoke_rcu_core(); /* force nohz to see update. */
|
|
rdtp->tick_nohz_enabled_snap = tne;
|
|
return;
|
|
}
|
|
if (!tne)
|
|
return;
|
|
|
|
/*
|
|
* If a non-lazy callback arrived at a CPU having only lazy
|
|
* callbacks, invoke RCU core for the side-effect of recalculating
|
|
* idle duration on re-entry to idle.
|
|
*/
|
|
if (rdtp->all_lazy &&
|
|
rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
|
|
rdtp->all_lazy = false;
|
|
rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
|
|
invoke_rcu_core();
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* If we have not yet accelerated this jiffy, accelerate all
|
|
* callbacks on this CPU.
|
|
*/
|
|
if (rdtp->last_accelerate == jiffies)
|
|
return;
|
|
rdtp->last_accelerate = jiffies;
|
|
for_each_rcu_flavor(rsp) {
|
|
rdp = this_cpu_ptr(rsp->rda);
|
|
if (rcu_segcblist_pend_cbs(&rdp->cblist))
|
|
continue;
|
|
rnp = rdp->mynode;
|
|
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
|
|
needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
|
|
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
|
|
if (needwake)
|
|
rcu_gp_kthread_wake(rsp);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Clean up for exit from idle. Attempt to advance callbacks based on
|
|
* any grace periods that elapsed while the CPU was idle, and if any
|
|
* callbacks are now ready to invoke, initiate invocation.
|
|
*/
|
|
static void rcu_cleanup_after_idle(void)
|
|
{
|
|
RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_cleanup_after_idle() invoked with irqs enabled!!!");
|
|
if (rcu_is_nocb_cpu(smp_processor_id()))
|
|
return;
|
|
if (rcu_try_advance_all_cbs())
|
|
invoke_rcu_core();
|
|
}
|
|
|
|
/*
|
|
* Keep a running count of the number of non-lazy callbacks posted
|
|
* on this CPU. This running counter (which is never decremented) allows
|
|
* rcu_prepare_for_idle() to detect when something out of the idle loop
|
|
* posts a callback, even if an equal number of callbacks are invoked.
|
|
* Of course, callbacks should only be posted from within a trace event
|
|
* designed to be called from idle or from within RCU_NONIDLE().
|
|
*/
|
|
static void rcu_idle_count_callbacks_posted(void)
|
|
{
|
|
__this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
|
|
}
|
|
|
|
/*
|
|
* Data for flushing lazy RCU callbacks at OOM time.
|
|
*/
|
|
static atomic_t oom_callback_count;
|
|
static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
|
|
|
|
/*
|
|
* RCU OOM callback -- decrement the outstanding count and deliver the
|
|
* wake-up if we are the last one.
|
|
*/
|
|
static void rcu_oom_callback(struct rcu_head *rhp)
|
|
{
|
|
if (atomic_dec_and_test(&oom_callback_count))
|
|
wake_up(&oom_callback_wq);
|
|
}
|
|
|
|
/*
|
|
* Post an rcu_oom_notify callback on the current CPU if it has at
|
|
* least one lazy callback. This will unnecessarily post callbacks
|
|
* to CPUs that already have a non-lazy callback at the end of their
|
|
* callback list, but this is an infrequent operation, so accept some
|
|
* extra overhead to keep things simple.
|
|
*/
|
|
static void rcu_oom_notify_cpu(void *unused)
|
|
{
|
|
struct rcu_state *rsp;
|
|
struct rcu_data *rdp;
|
|
|
|
for_each_rcu_flavor(rsp) {
|
|
rdp = raw_cpu_ptr(rsp->rda);
|
|
if (rcu_segcblist_n_lazy_cbs(&rdp->cblist)) {
|
|
atomic_inc(&oom_callback_count);
|
|
rsp->call(&rdp->oom_head, rcu_oom_callback);
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* If low on memory, ensure that each CPU has a non-lazy callback.
|
|
* This will wake up CPUs that have only lazy callbacks, in turn
|
|
* ensuring that they free up the corresponding memory in a timely manner.
|
|
* Because an uncertain amount of memory will be freed in some uncertain
|
|
* timeframe, we do not claim to have freed anything.
|
|
*/
|
|
static int rcu_oom_notify(struct notifier_block *self,
|
|
unsigned long notused, void *nfreed)
|
|
{
|
|
int cpu;
|
|
|
|
/* Wait for callbacks from earlier instance to complete. */
|
|
wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
|
|
smp_mb(); /* Ensure callback reuse happens after callback invocation. */
|
|
|
|
/*
|
|
* Prevent premature wakeup: ensure that all increments happen
|
|
* before there is a chance of the counter reaching zero.
|
|
*/
|
|
atomic_set(&oom_callback_count, 1);
|
|
|
|
for_each_online_cpu(cpu) {
|
|
smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
|
|
cond_resched_rcu_qs();
|
|
}
|
|
|
|
/* Unconditionally decrement: no need to wake ourselves up. */
|
|
atomic_dec(&oom_callback_count);
|
|
|
|
return NOTIFY_OK;
|
|
}
|
|
|
|
static struct notifier_block rcu_oom_nb = {
|
|
.notifier_call = rcu_oom_notify
|
|
};
|
|
|
|
static int __init rcu_register_oom_notifier(void)
|
|
{
|
|
register_oom_notifier(&rcu_oom_nb);
|
|
return 0;
|
|
}
|
|
early_initcall(rcu_register_oom_notifier);
|
|
|
|
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
|
|
|
|
#ifdef CONFIG_RCU_FAST_NO_HZ
|
|
|
|
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
|
|
{
|
|
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
|
|
unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
|
|
|
|
sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
|
|
rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
|
|
ulong2long(nlpd),
|
|
rdtp->all_lazy ? 'L' : '.',
|
|
rdtp->tick_nohz_enabled_snap ? '.' : 'D');
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
|
|
|
|
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
|
|
{
|
|
*cp = '\0';
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
|
|
|
|
/* Initiate the stall-info list. */
|
|
static void print_cpu_stall_info_begin(void)
|
|
{
|
|
pr_cont("\n");
|
|
}
|
|
|
|
/*
|
|
* Print out diagnostic information for the specified stalled CPU.
|
|
*
|
|
* If the specified CPU is aware of the current RCU grace period
|
|
* (flavor specified by rsp), then print the number of scheduling
|
|
* clock interrupts the CPU has taken during the time that it has
|
|
* been aware. Otherwise, print the number of RCU grace periods
|
|
* that this CPU is ignorant of, for example, "1" if the CPU was
|
|
* aware of the previous grace period.
|
|
*
|
|
* Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
|
|
*/
|
|
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
|
|
{
|
|
char fast_no_hz[72];
|
|
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
|
|
struct rcu_dynticks *rdtp = rdp->dynticks;
|
|
char *ticks_title;
|
|
unsigned long ticks_value;
|
|
|
|
if (rsp->gpnum == rdp->gpnum) {
|
|
ticks_title = "ticks this GP";
|
|
ticks_value = rdp->ticks_this_gp;
|
|
} else {
|
|
ticks_title = "GPs behind";
|
|
ticks_value = rsp->gpnum - rdp->gpnum;
|
|
}
|
|
print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
|
|
pr_err("\t%d-%c%c%c: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s\n",
|
|
cpu,
|
|
"O."[!!cpu_online(cpu)],
|
|
"o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
|
|
"N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
|
|
ticks_value, ticks_title,
|
|
rcu_dynticks_snap(rdtp) & 0xfff,
|
|
rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
|
|
rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
|
|
READ_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart,
|
|
fast_no_hz);
|
|
}
|
|
|
|
/* Terminate the stall-info list. */
|
|
static void print_cpu_stall_info_end(void)
|
|
{
|
|
pr_err("\t");
|
|
}
|
|
|
|
/* Zero ->ticks_this_gp for all flavors of RCU. */
|
|
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
|
|
{
|
|
rdp->ticks_this_gp = 0;
|
|
rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
|
|
}
|
|
|
|
/* Increment ->ticks_this_gp for all flavors of RCU. */
|
|
static void increment_cpu_stall_ticks(void)
|
|
{
|
|
struct rcu_state *rsp;
|
|
|
|
for_each_rcu_flavor(rsp)
|
|
raw_cpu_inc(rsp->rda->ticks_this_gp);
|
|
}
|
|
|
|
#ifdef CONFIG_RCU_NOCB_CPU
|
|
|
|
/*
|
|
* Offload callback processing from the boot-time-specified set of CPUs
|
|
* specified by rcu_nocb_mask. For each CPU in the set, there is a
|
|
* kthread created that pulls the callbacks from the corresponding CPU,
|
|
* waits for a grace period to elapse, and invokes the callbacks.
|
|
* The no-CBs CPUs do a wake_up() on their kthread when they insert
|
|
* a callback into any empty list, unless the rcu_nocb_poll boot parameter
|
|
* has been specified, in which case each kthread actively polls its
|
|
* CPU. (Which isn't so great for energy efficiency, but which does
|
|
* reduce RCU's overhead on that CPU.)
|
|
*
|
|
* This is intended to be used in conjunction with Frederic Weisbecker's
|
|
* adaptive-idle work, which would seriously reduce OS jitter on CPUs
|
|
* running CPU-bound user-mode computations.
|
|
*
|
|
* Offloading of callback processing could also in theory be used as
|
|
* an energy-efficiency measure because CPUs with no RCU callbacks
|
|
* queued are more aggressive about entering dyntick-idle mode.
|
|
*/
|
|
|
|
|
|
/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
|
|
static int __init rcu_nocb_setup(char *str)
|
|
{
|
|
alloc_bootmem_cpumask_var(&rcu_nocb_mask);
|
|
have_rcu_nocb_mask = true;
|
|
cpulist_parse(str, rcu_nocb_mask);
|
|
return 1;
|
|
}
|
|
__setup("rcu_nocbs=", rcu_nocb_setup);
|
|
|
|
static int __init parse_rcu_nocb_poll(char *arg)
|
|
{
|
|
rcu_nocb_poll = true;
|
|
return 0;
|
|
}
|
|
early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
|
|
|
|
/*
|
|
* Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
|
|
* grace period.
|
|
*/
|
|
static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
|
|
{
|
|
swake_up_all(sq);
|
|
}
|
|
|
|
/*
|
|
* Set the root rcu_node structure's ->need_future_gp field
|
|
* based on the sum of those of all rcu_node structures. This does
|
|
* double-count the root rcu_node structure's requests, but this
|
|
* is necessary to handle the possibility of a rcu_nocb_kthread()
|
|
* having awakened during the time that the rcu_node structures
|
|
* were being updated for the end of the previous grace period.
|
|
*/
|
|
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
|
|
{
|
|
rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
|
|
}
|
|
|
|
static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
|
|
{
|
|
return &rnp->nocb_gp_wq[rnp->completed & 0x1];
|
|
}
|
|
|
|
static void rcu_init_one_nocb(struct rcu_node *rnp)
|
|
{
|
|
init_swait_queue_head(&rnp->nocb_gp_wq[0]);
|
|
init_swait_queue_head(&rnp->nocb_gp_wq[1]);
|
|
}
|
|
|
|
/* Is the specified CPU a no-CBs CPU? */
|
|
bool rcu_is_nocb_cpu(int cpu)
|
|
{
|
|
if (have_rcu_nocb_mask)
|
|
return cpumask_test_cpu(cpu, rcu_nocb_mask);
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Kick the leader kthread for this NOCB group.
|
|
*/
|
|
static void wake_nocb_leader(struct rcu_data *rdp, bool force)
|
|
{
|
|
struct rcu_data *rdp_leader = rdp->nocb_leader;
|
|
|
|
if (!READ_ONCE(rdp_leader->nocb_kthread))
|
|
return;
|
|
if (READ_ONCE(rdp_leader->nocb_leader_sleep) || force) {
|
|
/* Prior smp_mb__after_atomic() orders against prior enqueue. */
|
|
WRITE_ONCE(rdp_leader->nocb_leader_sleep, false);
|
|
smp_mb(); /* ->nocb_leader_sleep before swake_up(). */
|
|
swake_up(&rdp_leader->nocb_wq);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Does the specified CPU need an RCU callback for the specified flavor
|
|
* of rcu_barrier()?
|
|
*/
|
|
static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
|
|
{
|
|
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
|
|
unsigned long ret;
|
|
#ifdef CONFIG_PROVE_RCU
|
|
struct rcu_head *rhp;
|
|
#endif /* #ifdef CONFIG_PROVE_RCU */
|
|
|
|
/*
|
|
* Check count of all no-CBs callbacks awaiting invocation.
|
|
* There needs to be a barrier before this function is called,
|
|
* but associated with a prior determination that no more
|
|
* callbacks would be posted. In the worst case, the first
|
|
* barrier in _rcu_barrier() suffices (but the caller cannot
|
|
* necessarily rely on this, not a substitute for the caller
|
|
* getting the concurrency design right!). There must also be
|
|
* a barrier between the following load an posting of a callback
|
|
* (if a callback is in fact needed). This is associated with an
|
|
* atomic_inc() in the caller.
|
|
*/
|
|
ret = atomic_long_read(&rdp->nocb_q_count);
|
|
|
|
#ifdef CONFIG_PROVE_RCU
|
|
rhp = READ_ONCE(rdp->nocb_head);
|
|
if (!rhp)
|
|
rhp = READ_ONCE(rdp->nocb_gp_head);
|
|
if (!rhp)
|
|
rhp = READ_ONCE(rdp->nocb_follower_head);
|
|
|
|
/* Having no rcuo kthread but CBs after scheduler starts is bad! */
|
|
if (!READ_ONCE(rdp->nocb_kthread) && rhp &&
|
|
rcu_scheduler_fully_active) {
|
|
/* RCU callback enqueued before CPU first came online??? */
|
|
pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
|
|
cpu, rhp->func);
|
|
WARN_ON_ONCE(1);
|
|
}
|
|
#endif /* #ifdef CONFIG_PROVE_RCU */
|
|
|
|
return !!ret;
|
|
}
|
|
|
|
/*
|
|
* Enqueue the specified string of rcu_head structures onto the specified
|
|
* CPU's no-CBs lists. The CPU is specified by rdp, the head of the
|
|
* string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
|
|
* counts are supplied by rhcount and rhcount_lazy.
|
|
*
|
|
* If warranted, also wake up the kthread servicing this CPUs queues.
|
|
*/
|
|
static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
|
|
struct rcu_head *rhp,
|
|
struct rcu_head **rhtp,
|
|
int rhcount, int rhcount_lazy,
|
|
unsigned long flags)
|
|
{
|
|
int len;
|
|
struct rcu_head **old_rhpp;
|
|
struct task_struct *t;
|
|
|
|
/* Enqueue the callback on the nocb list and update counts. */
|
|
atomic_long_add(rhcount, &rdp->nocb_q_count);
|
|
/* rcu_barrier() relies on ->nocb_q_count add before xchg. */
|
|
old_rhpp = xchg(&rdp->nocb_tail, rhtp);
|
|
WRITE_ONCE(*old_rhpp, rhp);
|
|
atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
|
|
smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
|
|
|
|
/* If we are not being polled and there is a kthread, awaken it ... */
|
|
t = READ_ONCE(rdp->nocb_kthread);
|
|
if (rcu_nocb_poll || !t) {
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
|
|
TPS("WakeNotPoll"));
|
|
return;
|
|
}
|
|
len = atomic_long_read(&rdp->nocb_q_count);
|
|
if (old_rhpp == &rdp->nocb_head) {
|
|
if (!irqs_disabled_flags(flags)) {
|
|
/* ... if queue was empty ... */
|
|
wake_nocb_leader(rdp, false);
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
|
|
TPS("WakeEmpty"));
|
|
} else {
|
|
WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE);
|
|
/* Store ->nocb_defer_wakeup before ->rcu_urgent_qs. */
|
|
smp_store_release(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs), true);
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
|
|
TPS("WakeEmptyIsDeferred"));
|
|
}
|
|
rdp->qlen_last_fqs_check = 0;
|
|
} else if (len > rdp->qlen_last_fqs_check + qhimark) {
|
|
/* ... or if many callbacks queued. */
|
|
if (!irqs_disabled_flags(flags)) {
|
|
wake_nocb_leader(rdp, true);
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
|
|
TPS("WakeOvf"));
|
|
} else {
|
|
WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_FORCE);
|
|
/* Store ->nocb_defer_wakeup before ->rcu_urgent_qs. */
|
|
smp_store_release(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs), true);
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
|
|
TPS("WakeOvfIsDeferred"));
|
|
}
|
|
rdp->qlen_last_fqs_check = LONG_MAX / 2;
|
|
} else {
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
|
|
}
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* This is a helper for __call_rcu(), which invokes this when the normal
|
|
* callback queue is inoperable. If this is not a no-CBs CPU, this
|
|
* function returns failure back to __call_rcu(), which can complain
|
|
* appropriately.
|
|
*
|
|
* Otherwise, this function queues the callback where the corresponding
|
|
* "rcuo" kthread can find it.
|
|
*/
|
|
static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
|
|
bool lazy, unsigned long flags)
|
|
{
|
|
|
|
if (!rcu_is_nocb_cpu(rdp->cpu))
|
|
return false;
|
|
__call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
|
|
if (__is_kfree_rcu_offset((unsigned long)rhp->func))
|
|
trace_rcu_kfree_callback(rdp->rsp->name, rhp,
|
|
(unsigned long)rhp->func,
|
|
-atomic_long_read(&rdp->nocb_q_count_lazy),
|
|
-atomic_long_read(&rdp->nocb_q_count));
|
|
else
|
|
trace_rcu_callback(rdp->rsp->name, rhp,
|
|
-atomic_long_read(&rdp->nocb_q_count_lazy),
|
|
-atomic_long_read(&rdp->nocb_q_count));
|
|
|
|
/*
|
|
* If called from an extended quiescent state with interrupts
|
|
* disabled, invoke the RCU core in order to allow the idle-entry
|
|
* deferred-wakeup check to function.
|
|
*/
|
|
if (irqs_disabled_flags(flags) &&
|
|
!rcu_is_watching() &&
|
|
cpu_online(smp_processor_id()))
|
|
invoke_rcu_core();
|
|
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
|
|
* not a no-CBs CPU.
|
|
*/
|
|
static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
|
|
struct rcu_data *rdp,
|
|
unsigned long flags)
|
|
{
|
|
long ql = rsp->orphan_done.len;
|
|
long qll = rsp->orphan_done.len_lazy;
|
|
|
|
/* If this is not a no-CBs CPU, tell the caller to do it the old way. */
|
|
if (!rcu_is_nocb_cpu(smp_processor_id()))
|
|
return false;
|
|
|
|
/* First, enqueue the donelist, if any. This preserves CB ordering. */
|
|
if (rsp->orphan_done.head) {
|
|
__call_rcu_nocb_enqueue(rdp, rcu_cblist_head(&rsp->orphan_done),
|
|
rcu_cblist_tail(&rsp->orphan_done),
|
|
ql, qll, flags);
|
|
}
|
|
if (rsp->orphan_pend.head) {
|
|
__call_rcu_nocb_enqueue(rdp, rcu_cblist_head(&rsp->orphan_pend),
|
|
rcu_cblist_tail(&rsp->orphan_pend),
|
|
ql, qll, flags);
|
|
}
|
|
rcu_cblist_init(&rsp->orphan_done);
|
|
rcu_cblist_init(&rsp->orphan_pend);
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* If necessary, kick off a new grace period, and either way wait
|
|
* for a subsequent grace period to complete.
|
|
*/
|
|
static void rcu_nocb_wait_gp(struct rcu_data *rdp)
|
|
{
|
|
unsigned long c;
|
|
bool d;
|
|
unsigned long flags;
|
|
bool needwake;
|
|
struct rcu_node *rnp = rdp->mynode;
|
|
|
|
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
|
needwake = rcu_start_future_gp(rnp, rdp, &c);
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
if (needwake)
|
|
rcu_gp_kthread_wake(rdp->rsp);
|
|
|
|
/*
|
|
* Wait for the grace period. Do so interruptibly to avoid messing
|
|
* up the load average.
|
|
*/
|
|
trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
|
|
for (;;) {
|
|
swait_event_interruptible(
|
|
rnp->nocb_gp_wq[c & 0x1],
|
|
(d = ULONG_CMP_GE(READ_ONCE(rnp->completed), c)));
|
|
if (likely(d))
|
|
break;
|
|
WARN_ON(signal_pending(current));
|
|
trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
|
|
}
|
|
trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
|
|
smp_mb(); /* Ensure that CB invocation happens after GP end. */
|
|
}
|
|
|
|
/*
|
|
* Leaders come here to wait for additional callbacks to show up.
|
|
* This function does not return until callbacks appear.
|
|
*/
|
|
static void nocb_leader_wait(struct rcu_data *my_rdp)
|
|
{
|
|
bool firsttime = true;
|
|
bool gotcbs;
|
|
struct rcu_data *rdp;
|
|
struct rcu_head **tail;
|
|
|
|
wait_again:
|
|
|
|
/* Wait for callbacks to appear. */
|
|
if (!rcu_nocb_poll) {
|
|
trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Sleep");
|
|
swait_event_interruptible(my_rdp->nocb_wq,
|
|
!READ_ONCE(my_rdp->nocb_leader_sleep));
|
|
/* Memory barrier handled by smp_mb() calls below and repoll. */
|
|
} else if (firsttime) {
|
|
firsttime = false; /* Don't drown trace log with "Poll"! */
|
|
trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Poll");
|
|
}
|
|
|
|
/*
|
|
* Each pass through the following loop checks a follower for CBs.
|
|
* We are our own first follower. Any CBs found are moved to
|
|
* nocb_gp_head, where they await a grace period.
|
|
*/
|
|
gotcbs = false;
|
|
smp_mb(); /* wakeup before ->nocb_head reads. */
|
|
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
|
|
rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head);
|
|
if (!rdp->nocb_gp_head)
|
|
continue; /* No CBs here, try next follower. */
|
|
|
|
/* Move callbacks to wait-for-GP list, which is empty. */
|
|
WRITE_ONCE(rdp->nocb_head, NULL);
|
|
rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
|
|
gotcbs = true;
|
|
}
|
|
|
|
/*
|
|
* If there were no callbacks, sleep a bit, rescan after a
|
|
* memory barrier, and go retry.
|
|
*/
|
|
if (unlikely(!gotcbs)) {
|
|
if (!rcu_nocb_poll)
|
|
trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
|
|
"WokeEmpty");
|
|
WARN_ON(signal_pending(current));
|
|
schedule_timeout_interruptible(1);
|
|
|
|
/* Rescan in case we were a victim of memory ordering. */
|
|
my_rdp->nocb_leader_sleep = true;
|
|
smp_mb(); /* Ensure _sleep true before scan. */
|
|
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower)
|
|
if (READ_ONCE(rdp->nocb_head)) {
|
|
/* Found CB, so short-circuit next wait. */
|
|
my_rdp->nocb_leader_sleep = false;
|
|
break;
|
|
}
|
|
goto wait_again;
|
|
}
|
|
|
|
/* Wait for one grace period. */
|
|
rcu_nocb_wait_gp(my_rdp);
|
|
|
|
/*
|
|
* We left ->nocb_leader_sleep unset to reduce cache thrashing.
|
|
* We set it now, but recheck for new callbacks while
|
|
* traversing our follower list.
|
|
*/
|
|
my_rdp->nocb_leader_sleep = true;
|
|
smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */
|
|
|
|
/* Each pass through the following loop wakes a follower, if needed. */
|
|
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
|
|
if (READ_ONCE(rdp->nocb_head))
|
|
my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/
|
|
if (!rdp->nocb_gp_head)
|
|
continue; /* No CBs, so no need to wake follower. */
|
|
|
|
/* Append callbacks to follower's "done" list. */
|
|
tail = xchg(&rdp->nocb_follower_tail, rdp->nocb_gp_tail);
|
|
*tail = rdp->nocb_gp_head;
|
|
smp_mb__after_atomic(); /* Store *tail before wakeup. */
|
|
if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
|
|
/*
|
|
* List was empty, wake up the follower.
|
|
* Memory barriers supplied by atomic_long_add().
|
|
*/
|
|
swake_up(&rdp->nocb_wq);
|
|
}
|
|
}
|
|
|
|
/* If we (the leader) don't have CBs, go wait some more. */
|
|
if (!my_rdp->nocb_follower_head)
|
|
goto wait_again;
|
|
}
|
|
|
|
/*
|
|
* Followers come here to wait for additional callbacks to show up.
|
|
* This function does not return until callbacks appear.
|
|
*/
|
|
static void nocb_follower_wait(struct rcu_data *rdp)
|
|
{
|
|
bool firsttime = true;
|
|
|
|
for (;;) {
|
|
if (!rcu_nocb_poll) {
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
|
|
"FollowerSleep");
|
|
swait_event_interruptible(rdp->nocb_wq,
|
|
READ_ONCE(rdp->nocb_follower_head));
|
|
} else if (firsttime) {
|
|
/* Don't drown trace log with "Poll"! */
|
|
firsttime = false;
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "Poll");
|
|
}
|
|
if (smp_load_acquire(&rdp->nocb_follower_head)) {
|
|
/* ^^^ Ensure CB invocation follows _head test. */
|
|
return;
|
|
}
|
|
if (!rcu_nocb_poll)
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
|
|
"WokeEmpty");
|
|
WARN_ON(signal_pending(current));
|
|
schedule_timeout_interruptible(1);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
|
|
* callbacks queued by the corresponding no-CBs CPU, however, there is
|
|
* an optional leader-follower relationship so that the grace-period
|
|
* kthreads don't have to do quite so many wakeups.
|
|
*/
|
|
static int rcu_nocb_kthread(void *arg)
|
|
{
|
|
int c, cl;
|
|
struct rcu_head *list;
|
|
struct rcu_head *next;
|
|
struct rcu_head **tail;
|
|
struct rcu_data *rdp = arg;
|
|
|
|
/* Each pass through this loop invokes one batch of callbacks */
|
|
for (;;) {
|
|
/* Wait for callbacks. */
|
|
if (rdp->nocb_leader == rdp)
|
|
nocb_leader_wait(rdp);
|
|
else
|
|
nocb_follower_wait(rdp);
|
|
|
|
/* Pull the ready-to-invoke callbacks onto local list. */
|
|
list = READ_ONCE(rdp->nocb_follower_head);
|
|
BUG_ON(!list);
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "WokeNonEmpty");
|
|
WRITE_ONCE(rdp->nocb_follower_head, NULL);
|
|
tail = xchg(&rdp->nocb_follower_tail, &rdp->nocb_follower_head);
|
|
|
|
/* Each pass through the following loop invokes a callback. */
|
|
trace_rcu_batch_start(rdp->rsp->name,
|
|
atomic_long_read(&rdp->nocb_q_count_lazy),
|
|
atomic_long_read(&rdp->nocb_q_count), -1);
|
|
c = cl = 0;
|
|
while (list) {
|
|
next = list->next;
|
|
/* Wait for enqueuing to complete, if needed. */
|
|
while (next == NULL && &list->next != tail) {
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
|
|
TPS("WaitQueue"));
|
|
schedule_timeout_interruptible(1);
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
|
|
TPS("WokeQueue"));
|
|
next = list->next;
|
|
}
|
|
debug_rcu_head_unqueue(list);
|
|
local_bh_disable();
|
|
if (__rcu_reclaim(rdp->rsp->name, list))
|
|
cl++;
|
|
c++;
|
|
local_bh_enable();
|
|
cond_resched_rcu_qs();
|
|
list = next;
|
|
}
|
|
trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
|
|
smp_mb__before_atomic(); /* _add after CB invocation. */
|
|
atomic_long_add(-c, &rdp->nocb_q_count);
|
|
atomic_long_add(-cl, &rdp->nocb_q_count_lazy);
|
|
rdp->n_nocbs_invoked += c;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/* Is a deferred wakeup of rcu_nocb_kthread() required? */
|
|
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
|
|
{
|
|
return READ_ONCE(rdp->nocb_defer_wakeup);
|
|
}
|
|
|
|
/* Do a deferred wakeup of rcu_nocb_kthread(). */
|
|
static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
|
|
{
|
|
int ndw;
|
|
|
|
if (!rcu_nocb_need_deferred_wakeup(rdp))
|
|
return;
|
|
ndw = READ_ONCE(rdp->nocb_defer_wakeup);
|
|
WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
|
|
wake_nocb_leader(rdp, ndw == RCU_NOCB_WAKE_FORCE);
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake"));
|
|
}
|
|
|
|
void __init rcu_init_nohz(void)
|
|
{
|
|
int cpu;
|
|
bool need_rcu_nocb_mask = true;
|
|
struct rcu_state *rsp;
|
|
|
|
#if defined(CONFIG_NO_HZ_FULL)
|
|
if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
|
|
need_rcu_nocb_mask = true;
|
|
#endif /* #if defined(CONFIG_NO_HZ_FULL) */
|
|
|
|
if (!have_rcu_nocb_mask && need_rcu_nocb_mask) {
|
|
if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
|
|
pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
|
|
return;
|
|
}
|
|
have_rcu_nocb_mask = true;
|
|
}
|
|
if (!have_rcu_nocb_mask)
|
|
return;
|
|
|
|
#if defined(CONFIG_NO_HZ_FULL)
|
|
if (tick_nohz_full_running)
|
|
cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
|
|
#endif /* #if defined(CONFIG_NO_HZ_FULL) */
|
|
|
|
if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
|
|
pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
|
|
cpumask_and(rcu_nocb_mask, cpu_possible_mask,
|
|
rcu_nocb_mask);
|
|
}
|
|
pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
|
|
cpumask_pr_args(rcu_nocb_mask));
|
|
if (rcu_nocb_poll)
|
|
pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
|
|
|
|
for_each_rcu_flavor(rsp) {
|
|
for_each_cpu(cpu, rcu_nocb_mask)
|
|
init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu));
|
|
rcu_organize_nocb_kthreads(rsp);
|
|
}
|
|
}
|
|
|
|
/* Initialize per-rcu_data variables for no-CBs CPUs. */
|
|
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
|
|
{
|
|
rdp->nocb_tail = &rdp->nocb_head;
|
|
init_swait_queue_head(&rdp->nocb_wq);
|
|
rdp->nocb_follower_tail = &rdp->nocb_follower_head;
|
|
}
|
|
|
|
/*
|
|
* If the specified CPU is a no-CBs CPU that does not already have its
|
|
* rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are
|
|
* brought online out of order, this can require re-organizing the
|
|
* leader-follower relationships.
|
|
*/
|
|
static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu)
|
|
{
|
|
struct rcu_data *rdp;
|
|
struct rcu_data *rdp_last;
|
|
struct rcu_data *rdp_old_leader;
|
|
struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu);
|
|
struct task_struct *t;
|
|
|
|
/*
|
|
* If this isn't a no-CBs CPU or if it already has an rcuo kthread,
|
|
* then nothing to do.
|
|
*/
|
|
if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread)
|
|
return;
|
|
|
|
/* If we didn't spawn the leader first, reorganize! */
|
|
rdp_old_leader = rdp_spawn->nocb_leader;
|
|
if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) {
|
|
rdp_last = NULL;
|
|
rdp = rdp_old_leader;
|
|
do {
|
|
rdp->nocb_leader = rdp_spawn;
|
|
if (rdp_last && rdp != rdp_spawn)
|
|
rdp_last->nocb_next_follower = rdp;
|
|
if (rdp == rdp_spawn) {
|
|
rdp = rdp->nocb_next_follower;
|
|
} else {
|
|
rdp_last = rdp;
|
|
rdp = rdp->nocb_next_follower;
|
|
rdp_last->nocb_next_follower = NULL;
|
|
}
|
|
} while (rdp);
|
|
rdp_spawn->nocb_next_follower = rdp_old_leader;
|
|
}
|
|
|
|
/* Spawn the kthread for this CPU and RCU flavor. */
|
|
t = kthread_run(rcu_nocb_kthread, rdp_spawn,
|
|
"rcuo%c/%d", rsp->abbr, cpu);
|
|
BUG_ON(IS_ERR(t));
|
|
WRITE_ONCE(rdp_spawn->nocb_kthread, t);
|
|
}
|
|
|
|
/*
|
|
* If the specified CPU is a no-CBs CPU that does not already have its
|
|
* rcuo kthreads, spawn them.
|
|
*/
|
|
static void rcu_spawn_all_nocb_kthreads(int cpu)
|
|
{
|
|
struct rcu_state *rsp;
|
|
|
|
if (rcu_scheduler_fully_active)
|
|
for_each_rcu_flavor(rsp)
|
|
rcu_spawn_one_nocb_kthread(rsp, cpu);
|
|
}
|
|
|
|
/*
|
|
* Once the scheduler is running, spawn rcuo kthreads for all online
|
|
* no-CBs CPUs. This assumes that the early_initcall()s happen before
|
|
* non-boot CPUs come online -- if this changes, we will need to add
|
|
* some mutual exclusion.
|
|
*/
|
|
static void __init rcu_spawn_nocb_kthreads(void)
|
|
{
|
|
int cpu;
|
|
|
|
for_each_online_cpu(cpu)
|
|
rcu_spawn_all_nocb_kthreads(cpu);
|
|
}
|
|
|
|
/* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */
|
|
static int rcu_nocb_leader_stride = -1;
|
|
module_param(rcu_nocb_leader_stride, int, 0444);
|
|
|
|
/*
|
|
* Initialize leader-follower relationships for all no-CBs CPU.
|
|
*/
|
|
static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp)
|
|
{
|
|
int cpu;
|
|
int ls = rcu_nocb_leader_stride;
|
|
int nl = 0; /* Next leader. */
|
|
struct rcu_data *rdp;
|
|
struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */
|
|
struct rcu_data *rdp_prev = NULL;
|
|
|
|
if (!have_rcu_nocb_mask)
|
|
return;
|
|
if (ls == -1) {
|
|
ls = int_sqrt(nr_cpu_ids);
|
|
rcu_nocb_leader_stride = ls;
|
|
}
|
|
|
|
/*
|
|
* Each pass through this loop sets up one rcu_data structure.
|
|
* Should the corresponding CPU come online in the future, then
|
|
* we will spawn the needed set of rcu_nocb_kthread() kthreads.
|
|
*/
|
|
for_each_cpu(cpu, rcu_nocb_mask) {
|
|
rdp = per_cpu_ptr(rsp->rda, cpu);
|
|
if (rdp->cpu >= nl) {
|
|
/* New leader, set up for followers & next leader. */
|
|
nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
|
|
rdp->nocb_leader = rdp;
|
|
rdp_leader = rdp;
|
|
} else {
|
|
/* Another follower, link to previous leader. */
|
|
rdp->nocb_leader = rdp_leader;
|
|
rdp_prev->nocb_next_follower = rdp;
|
|
}
|
|
rdp_prev = rdp;
|
|
}
|
|
}
|
|
|
|
/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
|
|
static bool init_nocb_callback_list(struct rcu_data *rdp)
|
|
{
|
|
if (!rcu_is_nocb_cpu(rdp->cpu))
|
|
return false;
|
|
|
|
/* If there are early-boot callbacks, move them to nocb lists. */
|
|
if (!rcu_segcblist_empty(&rdp->cblist)) {
|
|
rdp->nocb_head = rcu_segcblist_head(&rdp->cblist);
|
|
rdp->nocb_tail = rcu_segcblist_tail(&rdp->cblist);
|
|
atomic_long_set(&rdp->nocb_q_count,
|
|
rcu_segcblist_n_cbs(&rdp->cblist));
|
|
atomic_long_set(&rdp->nocb_q_count_lazy,
|
|
rcu_segcblist_n_lazy_cbs(&rdp->cblist));
|
|
rcu_segcblist_init(&rdp->cblist);
|
|
}
|
|
rcu_segcblist_disable(&rdp->cblist);
|
|
return true;
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
|
|
|
|
static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
|
|
{
|
|
WARN_ON_ONCE(1); /* Should be dead code. */
|
|
return false;
|
|
}
|
|
|
|
static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
|
|
{
|
|
}
|
|
|
|
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
|
|
{
|
|
}
|
|
|
|
static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
|
|
{
|
|
return NULL;
|
|
}
|
|
|
|
static void rcu_init_one_nocb(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
|
|
bool lazy, unsigned long flags)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
|
|
struct rcu_data *rdp,
|
|
unsigned long flags)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
static void rcu_spawn_all_nocb_kthreads(int cpu)
|
|
{
|
|
}
|
|
|
|
static void __init rcu_spawn_nocb_kthreads(void)
|
|
{
|
|
}
|
|
|
|
static bool init_nocb_callback_list(struct rcu_data *rdp)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
|
|
|
|
/*
|
|
* An adaptive-ticks CPU can potentially execute in kernel mode for an
|
|
* arbitrarily long period of time with the scheduling-clock tick turned
|
|
* off. RCU will be paying attention to this CPU because it is in the
|
|
* kernel, but the CPU cannot be guaranteed to be executing the RCU state
|
|
* machine because the scheduling-clock tick has been disabled. Therefore,
|
|
* if an adaptive-ticks CPU is failing to respond to the current grace
|
|
* period and has not be idle from an RCU perspective, kick it.
|
|
*/
|
|
static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
|
|
{
|
|
#ifdef CONFIG_NO_HZ_FULL
|
|
if (tick_nohz_full_cpu(cpu))
|
|
smp_send_reschedule(cpu);
|
|
#endif /* #ifdef CONFIG_NO_HZ_FULL */
|
|
}
|
|
|
|
/*
|
|
* Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
|
|
* grace-period kthread will do force_quiescent_state() processing?
|
|
* The idea is to avoid waking up RCU core processing on such a
|
|
* CPU unless the grace period has extended for too long.
|
|
*
|
|
* This code relies on the fact that all NO_HZ_FULL CPUs are also
|
|
* CONFIG_RCU_NOCB_CPU CPUs.
|
|
*/
|
|
static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
|
|
{
|
|
#ifdef CONFIG_NO_HZ_FULL
|
|
if (tick_nohz_full_cpu(smp_processor_id()) &&
|
|
(!rcu_gp_in_progress(rsp) ||
|
|
ULONG_CMP_LT(jiffies, READ_ONCE(rsp->gp_start) + HZ)))
|
|
return true;
|
|
#endif /* #ifdef CONFIG_NO_HZ_FULL */
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Bind the grace-period kthread for the sysidle flavor of RCU to the
|
|
* timekeeping CPU.
|
|
*/
|
|
static void rcu_bind_gp_kthread(void)
|
|
{
|
|
int __maybe_unused cpu;
|
|
|
|
if (!tick_nohz_full_enabled())
|
|
return;
|
|
housekeeping_affine(current);
|
|
}
|
|
|
|
/* Record the current task on dyntick-idle entry. */
|
|
static void rcu_dynticks_task_enter(void)
|
|
{
|
|
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
|
|
WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
|
|
#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
|
|
}
|
|
|
|
/* Record no current task on dyntick-idle exit. */
|
|
static void rcu_dynticks_task_exit(void)
|
|
{
|
|
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
|
|
WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
|
|
#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
|
|
}
|