srcu: Introduce CLASSIC_SRCU Kconfig option
The TREE_SRCU rewrite is large and a bit on the non-simple side, so this commit helps reduce risk by allowing the old v4.11 SRCU algorithm to be selected using a new CLASSIC_SRCU Kconfig option that depends on RCU_EXPERT. The default is to use the new TREE_SRCU and TINY_SRCU algorithms, in order to help get these the testing that they need. However, if your users do not require the update-side scalability that is to be provided by TREE_SRCU, select RCU_EXPERT and then CLASSIC_SRCU to revert back to the old classic SRCU algorithm. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney
Родитель
32071141b2
Коммит
dad81a2026
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@ -60,6 +60,8 @@ int init_srcu_struct(struct srcu_struct *sp);
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#include <linux/srcutiny.h>
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#elif defined(CONFIG_TREE_SRCU)
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#include <linux/srcutree.h>
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#elif defined(CONFIG_CLASSIC_SRCU)
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#include <linux/srcuclassic.h>
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#else
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#error "Unknown SRCU implementation specified to kernel configuration"
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#endif
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@ -0,0 +1,101 @@
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/*
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* Sleepable Read-Copy Update mechanism for mutual exclusion,
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* classic v4.11 variant.
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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 (C) IBM Corporation, 2017
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*
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* Author: Paul McKenney <paulmck@us.ibm.com>
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*/
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#ifndef _LINUX_SRCU_CLASSIC_H
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#define _LINUX_SRCU_CLASSIC_H
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struct srcu_array {
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unsigned long lock_count[2];
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unsigned long unlock_count[2];
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};
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struct rcu_batch {
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struct rcu_head *head, **tail;
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};
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#define RCU_BATCH_INIT(name) { NULL, &(name.head) }
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struct srcu_struct {
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unsigned long completed;
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struct srcu_array __percpu *per_cpu_ref;
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spinlock_t queue_lock; /* protect ->batch_queue, ->running */
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bool running;
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/* callbacks just queued */
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struct rcu_batch batch_queue;
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/* callbacks try to do the first check_zero */
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struct rcu_batch batch_check0;
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/* callbacks done with the first check_zero and the flip */
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struct rcu_batch batch_check1;
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struct rcu_batch batch_done;
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struct delayed_work work;
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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struct lockdep_map dep_map;
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#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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};
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void process_srcu(struct work_struct *work);
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#define __SRCU_STRUCT_INIT(name) \
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{ \
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.completed = -300, \
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.per_cpu_ref = &name##_srcu_array, \
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.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock), \
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.running = false, \
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.batch_queue = RCU_BATCH_INIT(name.batch_queue), \
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.batch_check0 = RCU_BATCH_INIT(name.batch_check0), \
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.batch_check1 = RCU_BATCH_INIT(name.batch_check1), \
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.batch_done = RCU_BATCH_INIT(name.batch_done), \
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.work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
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__SRCU_DEP_MAP_INIT(name) \
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}
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/*
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* Define and initialize a srcu struct at build time.
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* Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
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*
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* Note that although DEFINE_STATIC_SRCU() hides the name from other
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* files, the per-CPU variable rules nevertheless require that the
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* chosen name be globally unique. These rules also prohibit use of
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* DEFINE_STATIC_SRCU() within a function. If these rules are too
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* restrictive, declare the srcu_struct manually. For example, in
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* each file:
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*
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* static struct srcu_struct my_srcu;
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*
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* Then, before the first use of each my_srcu, manually initialize it:
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*
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* init_srcu_struct(&my_srcu);
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*
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* See include/linux/percpu-defs.h for the rules on per-CPU variables.
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*/
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#define __DEFINE_SRCU(name, is_static) \
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static DEFINE_PER_CPU(struct srcu_array, name##_srcu_array);\
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is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
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#define DEFINE_SRCU(name) __DEFINE_SRCU(name, /* not static */)
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#define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, static)
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void synchronize_srcu_expedited(struct srcu_struct *sp);
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void srcu_barrier(struct srcu_struct *sp);
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unsigned long srcu_batches_completed(struct srcu_struct *sp);
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#endif
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21
init/Kconfig
21
init/Kconfig
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@ -526,15 +526,32 @@ config SRCU
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permits arbitrary sleeping or blocking within RCU read-side critical
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sections.
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config CLASSIC_SRCU
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bool "Use v4.11 classic SRCU implementation"
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default n
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depends on RCU_EXPERT && SRCU
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help
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This option selects the traditional well-tested classic SRCU
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implementation from v4.11, as might be desired for enterprise
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Linux distributions. Without this option, the shiny new
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Tiny SRCU and Tree SRCU implementations are used instead.
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At some point, it is hoped that Tiny SRCU and Tree SRCU
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will accumulate enough test time and confidence to allow
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Classic SRCU to be dropped entirely.
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Say Y if you need a rock-solid SRCU.
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Say N if you would like help test Tree SRCU.
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config TINY_SRCU
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bool
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default y if TINY_RCU
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default y if TINY_RCU && !CLASSIC_SRCU
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help
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This option selects the single-CPU non-preemptible version of SRCU.
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config TREE_SRCU
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bool
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default y if !TINY_RCU
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default y if !TINY_RCU && !CLASSIC_SRCU
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help
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This option selects the full-fledged version of SRCU.
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@ -3,7 +3,8 @@
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KCOV_INSTRUMENT := n
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obj-y += update.o sync.o
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obj-$(CONFIG_TREE_SRCU) += srcu.o
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obj-$(CONFIG_CLASSIC_SRCU) += srcu.o
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obj-$(CONFIG_TREE_SRCU) += srcutree.o
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obj-$(CONFIG_TINY_SRCU) += srcutiny.o
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obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
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obj-$(CONFIG_RCU_PERF_TEST) += rcuperf.o
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@ -562,7 +562,7 @@ static void srcu_torture_stats(void)
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int __maybe_unused cpu;
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int idx;
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#ifdef CONFIG_TREE_SRCU
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#if defined(CONFIG_TREE_SRCU) || defined(CONFIG_CLASSIC_SRCU)
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idx = srcu_ctlp->completed & 0x1;
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pr_alert("%s%s Tree SRCU per-CPU(idx=%d):",
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torture_type, TORTURE_FLAG, idx);
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@ -36,16 +36,75 @@
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#include <linux/delay.h>
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#include <linux/srcu.h>
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#include <linux/rcu_node_tree.h>
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#include "rcu.h"
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/*
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* Initialize an rcu_batch structure to empty.
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*/
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static inline void rcu_batch_init(struct rcu_batch *b)
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{
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b->head = NULL;
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b->tail = &b->head;
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}
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/*
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* Enqueue a callback onto the tail of the specified rcu_batch structure.
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*/
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static inline void rcu_batch_queue(struct rcu_batch *b, struct rcu_head *head)
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{
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*b->tail = head;
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b->tail = &head->next;
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}
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/*
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* Is the specified rcu_batch structure empty?
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*/
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static inline bool rcu_batch_empty(struct rcu_batch *b)
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{
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return b->tail == &b->head;
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}
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/*
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* Remove the callback at the head of the specified rcu_batch structure
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* and return a pointer to it, or return NULL if the structure is empty.
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*/
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static inline struct rcu_head *rcu_batch_dequeue(struct rcu_batch *b)
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{
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struct rcu_head *head;
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if (rcu_batch_empty(b))
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return NULL;
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head = b->head;
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b->head = head->next;
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if (b->tail == &head->next)
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rcu_batch_init(b);
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return head;
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}
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/*
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* Move all callbacks from the rcu_batch structure specified by "from" to
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* the structure specified by "to".
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*/
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static inline void rcu_batch_move(struct rcu_batch *to, struct rcu_batch *from)
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{
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if (!rcu_batch_empty(from)) {
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*to->tail = from->head;
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to->tail = from->tail;
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rcu_batch_init(from);
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}
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}
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static int init_srcu_struct_fields(struct srcu_struct *sp)
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{
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sp->completed = 0;
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sp->srcu_gp_seq = 0;
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atomic_set(&sp->srcu_exp_cnt, 0);
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spin_lock_init(&sp->queue_lock);
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rcu_segcblist_init(&sp->srcu_cblist);
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sp->running = false;
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rcu_batch_init(&sp->batch_queue);
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rcu_batch_init(&sp->batch_check0);
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rcu_batch_init(&sp->batch_check1);
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rcu_batch_init(&sp->batch_done);
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INIT_DELAYED_WORK(&sp->work, process_srcu);
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sp->per_cpu_ref = alloc_percpu(struct srcu_array);
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return sp->per_cpu_ref ? 0 : -ENOMEM;
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@ -180,8 +239,6 @@ static bool srcu_readers_active(struct srcu_struct *sp)
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return sum;
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}
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#define SRCU_INTERVAL 1
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/**
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* cleanup_srcu_struct - deconstruct a sleep-RCU structure
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* @sp: structure to clean up.
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@ -197,16 +254,8 @@ static bool srcu_readers_active(struct srcu_struct *sp)
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*/
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void cleanup_srcu_struct(struct srcu_struct *sp)
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{
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WARN_ON_ONCE(atomic_read(&sp->srcu_exp_cnt));
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if (WARN_ON(srcu_readers_active(sp)))
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return; /* Leakage unless caller handles error. */
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if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist)))
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return; /* Leakage unless caller handles error. */
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flush_delayed_work(&sp->work);
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if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE)) {
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pr_info("cleanup_srcu_struct: Active srcu_struct %lu CBs %c state: %d\n", rcu_segcblist_n_cbs(&sp->srcu_cblist), ".E"[rcu_segcblist_empty(&sp->srcu_cblist)], rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
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return; /* Caller forgot to stop doing call_srcu()? */
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}
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free_percpu(sp->per_cpu_ref);
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sp->per_cpu_ref = NULL;
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}
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@ -245,36 +294,26 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
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* We use an adaptive strategy for synchronize_srcu() and especially for
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* synchronize_srcu_expedited(). We spin for a fixed time period
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* (defined below) to allow SRCU readers to exit their read-side critical
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* sections. If there are still some readers after a few microseconds,
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* we repeatedly block for 1-millisecond time periods.
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* sections. If there are still some readers after 10 microseconds,
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* we repeatedly block for 1-millisecond time periods. This approach
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* has done well in testing, so there is no need for a config parameter.
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*/
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#define SRCU_RETRY_CHECK_DELAY 5
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#define SYNCHRONIZE_SRCU_TRYCOUNT 2
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#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT 12
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/*
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* Start an SRCU grace period.
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*/
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static void srcu_gp_start(struct srcu_struct *sp)
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{
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int state;
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rcu_segcblist_accelerate(&sp->srcu_cblist,
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rcu_seq_snap(&sp->srcu_gp_seq));
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rcu_seq_start(&sp->srcu_gp_seq);
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state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
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WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
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}
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/*
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* Wait until all readers counted by array index idx complete, but
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* loop an additional time if there is an expedited grace period pending.
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* The caller must ensure that ->completed is not changed while checking.
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* @@@ Wait until all pre-existing readers complete. Such readers
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* will have used the index specified by "idx".
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* the caller should ensures the ->completed is not changed while checking
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* and idx = (->completed & 1) ^ 1
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*/
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static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
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{
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for (;;) {
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if (srcu_readers_active_idx_check(sp, idx))
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return true;
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if (--trycount + !!atomic_read(&sp->srcu_exp_cnt) <= 0)
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if (--trycount <= 0)
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return false;
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udelay(SRCU_RETRY_CHECK_DELAY);
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}
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@ -299,19 +338,6 @@ static void srcu_flip(struct srcu_struct *sp)
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smp_mb(); /* D */ /* Pairs with C. */
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}
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/*
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* End an SRCU grace period.
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*/
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static void srcu_gp_end(struct srcu_struct *sp)
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{
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rcu_seq_end(&sp->srcu_gp_seq);
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spin_lock_irq(&sp->queue_lock);
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rcu_segcblist_advance(&sp->srcu_cblist,
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rcu_seq_current(&sp->srcu_gp_seq));
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spin_unlock_irq(&sp->queue_lock);
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}
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/*
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* Enqueue an SRCU callback on the specified srcu_struct structure,
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* initiating grace-period processing if it is not already running.
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@ -348,24 +374,26 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
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head->func = func;
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spin_lock_irqsave(&sp->queue_lock, flags);
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smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
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rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
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if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
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srcu_gp_start(sp);
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rcu_batch_queue(&sp->batch_queue, head);
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if (!sp->running) {
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sp->running = true;
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queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
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}
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spin_unlock_irqrestore(&sp->queue_lock, flags);
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}
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EXPORT_SYMBOL_GPL(call_srcu);
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static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);
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static void srcu_advance_batches(struct srcu_struct *sp, int trycount);
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static void srcu_reschedule(struct srcu_struct *sp);
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/*
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* Helper function for synchronize_srcu() and synchronize_srcu_expedited().
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*/
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static void __synchronize_srcu(struct srcu_struct *sp)
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static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
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{
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struct rcu_synchronize rcu;
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struct rcu_head *head = &rcu.head;
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bool done = false;
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RCU_LOCKDEP_WARN(lock_is_held(&sp->dep_map) ||
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lock_is_held(&rcu_bh_lock_map) ||
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@ -373,8 +401,6 @@ static void __synchronize_srcu(struct srcu_struct *sp)
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lock_is_held(&rcu_sched_lock_map),
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"Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
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if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
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return;
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might_sleep();
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init_completion(&rcu.completion);
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@ -382,47 +408,31 @@ static void __synchronize_srcu(struct srcu_struct *sp)
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head->func = wakeme_after_rcu;
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spin_lock_irq(&sp->queue_lock);
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smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
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if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
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if (!sp->running) {
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/* steal the processing owner */
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rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
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srcu_gp_start(sp);
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sp->running = true;
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rcu_batch_queue(&sp->batch_check0, head);
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spin_unlock_irq(&sp->queue_lock);
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srcu_advance_batches(sp, trycount);
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if (!rcu_batch_empty(&sp->batch_done)) {
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BUG_ON(sp->batch_done.head != head);
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rcu_batch_dequeue(&sp->batch_done);
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done = true;
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}
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/* give the processing owner to work_struct */
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srcu_reschedule(sp, 0);
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srcu_reschedule(sp);
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} else {
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rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
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rcu_batch_queue(&sp->batch_queue, head);
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spin_unlock_irq(&sp->queue_lock);
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}
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wait_for_completion(&rcu.completion);
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smp_mb(); /* Caller's later accesses after GP. */
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}
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/**
|
||||
* synchronize_srcu_expedited - Brute-force SRCU grace period
|
||||
* @sp: srcu_struct with which to synchronize.
|
||||
*
|
||||
* Wait for an SRCU grace period to elapse, but be more aggressive about
|
||||
* spinning rather than blocking when waiting.
|
||||
*
|
||||
* Note that synchronize_srcu_expedited() has the same deadlock and
|
||||
* memory-ordering properties as does synchronize_srcu().
|
||||
*/
|
||||
void synchronize_srcu_expedited(struct srcu_struct *sp)
|
||||
{
|
||||
bool do_norm = rcu_gp_is_normal();
|
||||
|
||||
if (!do_norm) {
|
||||
atomic_inc(&sp->srcu_exp_cnt);
|
||||
smp_mb__after_atomic(); /* increment before GP. */
|
||||
}
|
||||
__synchronize_srcu(sp);
|
||||
if (!do_norm) {
|
||||
smp_mb__before_atomic(); /* GP before decrement. */
|
||||
atomic_dec(&sp->srcu_exp_cnt);
|
||||
if (!done) {
|
||||
wait_for_completion(&rcu.completion);
|
||||
smp_mb(); /* Caller's later accesses after GP. */
|
||||
}
|
||||
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
|
||||
|
||||
/**
|
||||
* synchronize_srcu - wait for prior SRCU read-side critical-section completion
|
||||
|
|
@ -465,13 +475,28 @@ EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
|
|||
*/
|
||||
void synchronize_srcu(struct srcu_struct *sp)
|
||||
{
|
||||
if (rcu_gp_is_expedited())
|
||||
synchronize_srcu_expedited(sp);
|
||||
else
|
||||
__synchronize_srcu(sp);
|
||||
__synchronize_srcu(sp, (rcu_gp_is_expedited() && !rcu_gp_is_normal())
|
||||
? SYNCHRONIZE_SRCU_EXP_TRYCOUNT
|
||||
: SYNCHRONIZE_SRCU_TRYCOUNT);
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(synchronize_srcu);
|
||||
|
||||
/**
|
||||
* synchronize_srcu_expedited - Brute-force SRCU grace period
|
||||
* @sp: srcu_struct with which to synchronize.
|
||||
*
|
||||
* Wait for an SRCU grace period to elapse, but be more aggressive about
|
||||
* spinning rather than blocking when waiting.
|
||||
*
|
||||
* Note that synchronize_srcu_expedited() has the same deadlock and
|
||||
* memory-ordering properties as does synchronize_srcu().
|
||||
*/
|
||||
void synchronize_srcu_expedited(struct srcu_struct *sp)
|
||||
{
|
||||
__synchronize_srcu(sp, SYNCHRONIZE_SRCU_EXP_TRYCOUNT);
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
|
||||
|
||||
/**
|
||||
* srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
|
||||
* @sp: srcu_struct on which to wait for in-flight callbacks.
|
||||
|
|
@ -495,13 +520,29 @@ unsigned long srcu_batches_completed(struct srcu_struct *sp)
|
|||
}
|
||||
EXPORT_SYMBOL_GPL(srcu_batches_completed);
|
||||
|
||||
#define SRCU_CALLBACK_BATCH 10
|
||||
#define SRCU_INTERVAL 1
|
||||
|
||||
/*
|
||||
* Move any new SRCU callbacks to the first stage of the SRCU grace
|
||||
* period pipeline.
|
||||
*/
|
||||
static void srcu_collect_new(struct srcu_struct *sp)
|
||||
{
|
||||
if (!rcu_batch_empty(&sp->batch_queue)) {
|
||||
spin_lock_irq(&sp->queue_lock);
|
||||
rcu_batch_move(&sp->batch_check0, &sp->batch_queue);
|
||||
spin_unlock_irq(&sp->queue_lock);
|
||||
}
|
||||
}
|
||||
|
||||
/*
|
||||
* Core SRCU state machine. Advance callbacks from ->batch_check0 to
|
||||
* ->batch_check1 and then to ->batch_done as readers drain.
|
||||
*/
|
||||
static void srcu_advance_batches(struct srcu_struct *sp)
|
||||
static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
|
||||
{
|
||||
int idx;
|
||||
int idx = 1 ^ (sp->completed & 1);
|
||||
|
||||
/*
|
||||
* Because readers might be delayed for an extended period after
|
||||
|
|
@ -509,44 +550,50 @@ static void srcu_advance_batches(struct srcu_struct *sp)
|
|||
* might well be readers using both idx=0 and idx=1. We therefore
|
||||
* need to wait for readers to clear from both index values before
|
||||
* invoking a callback.
|
||||
*
|
||||
* The load-acquire ensures that we see the accesses performed
|
||||
* by the prior grace period.
|
||||
*/
|
||||
idx = rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq)); /* ^^^ */
|
||||
if (idx == SRCU_STATE_IDLE) {
|
||||
spin_lock_irq(&sp->queue_lock);
|
||||
if (rcu_segcblist_empty(&sp->srcu_cblist)) {
|
||||
spin_unlock_irq(&sp->queue_lock);
|
||||
return;
|
||||
}
|
||||
idx = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
|
||||
if (idx == SRCU_STATE_IDLE)
|
||||
srcu_gp_start(sp);
|
||||
spin_unlock_irq(&sp->queue_lock);
|
||||
if (idx != SRCU_STATE_IDLE)
|
||||
return; /* Someone else started the grace period. */
|
||||
}
|
||||
|
||||
if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
|
||||
idx = 1 ^ (sp->completed & 1);
|
||||
if (!try_check_zero(sp, idx, 1))
|
||||
return; /* readers present, retry later. */
|
||||
srcu_flip(sp);
|
||||
rcu_seq_set_state(&sp->srcu_gp_seq, SRCU_STATE_SCAN2);
|
||||
}
|
||||
if (rcu_batch_empty(&sp->batch_check0) &&
|
||||
rcu_batch_empty(&sp->batch_check1))
|
||||
return; /* no callbacks need to be advanced */
|
||||
|
||||
if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN2) {
|
||||
if (!try_check_zero(sp, idx, trycount))
|
||||
return; /* failed to advance, will try after SRCU_INTERVAL */
|
||||
|
||||
/*
|
||||
* SRCU read-side critical sections are normally short,
|
||||
* so check at least twice in quick succession after a flip.
|
||||
*/
|
||||
idx = 1 ^ (sp->completed & 1);
|
||||
if (!try_check_zero(sp, idx, 2))
|
||||
return; /* readers present, retry after later. */
|
||||
srcu_gp_end(sp);
|
||||
}
|
||||
/*
|
||||
* The callbacks in ->batch_check1 have already done with their
|
||||
* first zero check and flip back when they were enqueued on
|
||||
* ->batch_check0 in a previous invocation of srcu_advance_batches().
|
||||
* (Presumably try_check_zero() returned false during that
|
||||
* invocation, leaving the callbacks stranded on ->batch_check1.)
|
||||
* They are therefore ready to invoke, so move them to ->batch_done.
|
||||
*/
|
||||
rcu_batch_move(&sp->batch_done, &sp->batch_check1);
|
||||
|
||||
if (rcu_batch_empty(&sp->batch_check0))
|
||||
return; /* no callbacks need to be advanced */
|
||||
srcu_flip(sp);
|
||||
|
||||
/*
|
||||
* The callbacks in ->batch_check0 just finished their
|
||||
* first check zero and flip, so move them to ->batch_check1
|
||||
* for future checking on the other idx.
|
||||
*/
|
||||
rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
|
||||
|
||||
/*
|
||||
* SRCU read-side critical sections are normally short, so check
|
||||
* at least twice in quick succession after a flip.
|
||||
*/
|
||||
trycount = trycount < 2 ? 2 : trycount;
|
||||
if (!try_check_zero(sp, idx^1, trycount))
|
||||
return; /* failed to advance, will try after SRCU_INTERVAL */
|
||||
|
||||
/*
|
||||
* The callbacks in ->batch_check1 have now waited for all
|
||||
* pre-existing readers using both idx values. They are therefore
|
||||
* ready to invoke, so move them to ->batch_done.
|
||||
*/
|
||||
rcu_batch_move(&sp->batch_done, &sp->batch_check1);
|
||||
}
|
||||
|
||||
/*
|
||||
|
|
@ -557,48 +604,45 @@ static void srcu_advance_batches(struct srcu_struct *sp)
|
|||
*/
|
||||
static void srcu_invoke_callbacks(struct srcu_struct *sp)
|
||||
{
|
||||
struct rcu_cblist ready_cbs;
|
||||
struct rcu_head *rhp;
|
||||
int i;
|
||||
struct rcu_head *head;
|
||||
|
||||
spin_lock_irq(&sp->queue_lock);
|
||||
if (!rcu_segcblist_ready_cbs(&sp->srcu_cblist)) {
|
||||
spin_unlock_irq(&sp->queue_lock);
|
||||
return;
|
||||
}
|
||||
rcu_cblist_init(&ready_cbs);
|
||||
rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs);
|
||||
spin_unlock_irq(&sp->queue_lock);
|
||||
rhp = rcu_cblist_dequeue(&ready_cbs);
|
||||
for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
|
||||
for (i = 0; i < SRCU_CALLBACK_BATCH; i++) {
|
||||
head = rcu_batch_dequeue(&sp->batch_done);
|
||||
if (!head)
|
||||
break;
|
||||
local_bh_disable();
|
||||
rhp->func(rhp);
|
||||
head->func(head);
|
||||
local_bh_enable();
|
||||
}
|
||||
spin_lock_irq(&sp->queue_lock);
|
||||
rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs);
|
||||
spin_unlock_irq(&sp->queue_lock);
|
||||
}
|
||||
|
||||
/*
|
||||
* Finished one round of SRCU grace period. Start another if there are
|
||||
* more SRCU callbacks queued, otherwise put SRCU into not-running state.
|
||||
*/
|
||||
static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
|
||||
static void srcu_reschedule(struct srcu_struct *sp)
|
||||
{
|
||||
bool pending = true;
|
||||
int state;
|
||||
|
||||
if (rcu_segcblist_empty(&sp->srcu_cblist)) {
|
||||
if (rcu_batch_empty(&sp->batch_done) &&
|
||||
rcu_batch_empty(&sp->batch_check1) &&
|
||||
rcu_batch_empty(&sp->batch_check0) &&
|
||||
rcu_batch_empty(&sp->batch_queue)) {
|
||||
spin_lock_irq(&sp->queue_lock);
|
||||
state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
|
||||
if (rcu_segcblist_empty(&sp->srcu_cblist) &&
|
||||
state == SRCU_STATE_IDLE)
|
||||
if (rcu_batch_empty(&sp->batch_done) &&
|
||||
rcu_batch_empty(&sp->batch_check1) &&
|
||||
rcu_batch_empty(&sp->batch_check0) &&
|
||||
rcu_batch_empty(&sp->batch_queue)) {
|
||||
sp->running = false;
|
||||
pending = false;
|
||||
}
|
||||
spin_unlock_irq(&sp->queue_lock);
|
||||
}
|
||||
|
||||
if (pending)
|
||||
queue_delayed_work(system_power_efficient_wq, &sp->work, delay);
|
||||
queue_delayed_work(system_power_efficient_wq,
|
||||
&sp->work, SRCU_INTERVAL);
|
||||
}
|
||||
|
||||
/*
|
||||
|
|
@ -610,8 +654,9 @@ void process_srcu(struct work_struct *work)
|
|||
|
||||
sp = container_of(work, struct srcu_struct, work.work);
|
||||
|
||||
srcu_advance_batches(sp);
|
||||
srcu_collect_new(sp);
|
||||
srcu_advance_batches(sp, 1);
|
||||
srcu_invoke_callbacks(sp);
|
||||
srcu_reschedule(sp, atomic_read(&sp->srcu_exp_cnt) ? 0 : SRCU_INTERVAL);
|
||||
srcu_reschedule(sp);
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(process_srcu);
|
||||
|
|
|
|||
|
|
@ -0,0 +1,613 @@
|
|||
/*
|
||||
* Sleepable Read-Copy Update mechanism for mutual exclusion.
|
||||
*
|
||||
* This program is free software; you can redistribute it and/or modify
|
||||
* it under the terms of the GNU General Public License as published by
|
||||
* the Free Software Foundation; either version 2 of the License, or
|
||||
* (at your option) any later version.
|
||||
*
|
||||
* This program is distributed in the hope that it will be useful,
|
||||
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||||
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||||
* GNU General Public License for more details.
|
||||
*
|
||||
* You should have received a copy of the GNU General Public License
|
||||
* along with this program; if not, you can access it online at
|
||||
* http://www.gnu.org/licenses/gpl-2.0.html.
|
||||
*
|
||||
* Copyright (C) IBM Corporation, 2006
|
||||
* Copyright (C) Fujitsu, 2012
|
||||
*
|
||||
* Author: Paul McKenney <paulmck@us.ibm.com>
|
||||
* Lai Jiangshan <laijs@cn.fujitsu.com>
|
||||
*
|
||||
* For detailed explanation of Read-Copy Update mechanism see -
|
||||
* Documentation/RCU/ *.txt
|
||||
*
|
||||
*/
|
||||
|
||||
#include <linux/export.h>
|
||||
#include <linux/mutex.h>
|
||||
#include <linux/percpu.h>
|
||||
#include <linux/preempt.h>
|
||||
#include <linux/rcupdate_wait.h>
|
||||
#include <linux/sched.h>
|
||||
#include <linux/smp.h>
|
||||
#include <linux/delay.h>
|
||||
#include <linux/srcu.h>
|
||||
|
||||
#include <linux/rcu_node_tree.h>
|
||||
#include "rcu.h"
|
||||
|
||||
static int init_srcu_struct_fields(struct srcu_struct *sp)
|
||||
{
|
||||
sp->completed = 0;
|
||||
sp->srcu_gp_seq = 0;
|
||||
atomic_set(&sp->srcu_exp_cnt, 0);
|
||||
spin_lock_init(&sp->queue_lock);
|
||||
rcu_segcblist_init(&sp->srcu_cblist);
|
||||
INIT_DELAYED_WORK(&sp->work, process_srcu);
|
||||
sp->per_cpu_ref = alloc_percpu(struct srcu_array);
|
||||
return sp->per_cpu_ref ? 0 : -ENOMEM;
|
||||
}
|
||||
|
||||
#ifdef CONFIG_DEBUG_LOCK_ALLOC
|
||||
|
||||
int __init_srcu_struct(struct srcu_struct *sp, const char *name,
|
||||
struct lock_class_key *key)
|
||||
{
|
||||
/* Don't re-initialize a lock while it is held. */
|
||||
debug_check_no_locks_freed((void *)sp, sizeof(*sp));
|
||||
lockdep_init_map(&sp->dep_map, name, key, 0);
|
||||
return init_srcu_struct_fields(sp);
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(__init_srcu_struct);
|
||||
|
||||
#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
|
||||
|
||||
/**
|
||||
* init_srcu_struct - initialize a sleep-RCU structure
|
||||
* @sp: structure to initialize.
|
||||
*
|
||||
* Must invoke this on a given srcu_struct before passing that srcu_struct
|
||||
* to any other function. Each srcu_struct represents a separate domain
|
||||
* of SRCU protection.
|
||||
*/
|
||||
int init_srcu_struct(struct srcu_struct *sp)
|
||||
{
|
||||
return init_srcu_struct_fields(sp);
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(init_srcu_struct);
|
||||
|
||||
#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
|
||||
|
||||
/*
|
||||
* Returns approximate total of the readers' ->lock_count[] values for the
|
||||
* rank of per-CPU counters specified by idx.
|
||||
*/
|
||||
static unsigned long srcu_readers_lock_idx(struct srcu_struct *sp, int idx)
|
||||
{
|
||||
int cpu;
|
||||
unsigned long sum = 0;
|
||||
|
||||
for_each_possible_cpu(cpu) {
|
||||
struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu);
|
||||
|
||||
sum += READ_ONCE(cpuc->lock_count[idx]);
|
||||
}
|
||||
return sum;
|
||||
}
|
||||
|
||||
/*
|
||||
* Returns approximate total of the readers' ->unlock_count[] values for the
|
||||
* rank of per-CPU counters specified by idx.
|
||||
*/
|
||||
static unsigned long srcu_readers_unlock_idx(struct srcu_struct *sp, int idx)
|
||||
{
|
||||
int cpu;
|
||||
unsigned long sum = 0;
|
||||
|
||||
for_each_possible_cpu(cpu) {
|
||||
struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu);
|
||||
|
||||
sum += READ_ONCE(cpuc->unlock_count[idx]);
|
||||
}
|
||||
return sum;
|
||||
}
|
||||
|
||||
/*
|
||||
* Return true if the number of pre-existing readers is determined to
|
||||
* be zero.
|
||||
*/
|
||||
static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
|
||||
{
|
||||
unsigned long unlocks;
|
||||
|
||||
unlocks = srcu_readers_unlock_idx(sp, idx);
|
||||
|
||||
/*
|
||||
* Make sure that a lock is always counted if the corresponding
|
||||
* unlock is counted. Needs to be a smp_mb() as the read side may
|
||||
* contain a read from a variable that is written to before the
|
||||
* synchronize_srcu() in the write side. In this case smp_mb()s
|
||||
* A and B act like the store buffering pattern.
|
||||
*
|
||||
* This smp_mb() also pairs with smp_mb() C to prevent accesses
|
||||
* after the synchronize_srcu() from being executed before the
|
||||
* grace period ends.
|
||||
*/
|
||||
smp_mb(); /* A */
|
||||
|
||||
/*
|
||||
* If the locks are the same as the unlocks, then there must have
|
||||
* been no readers on this index at some time in between. This does
|
||||
* not mean that there are no more readers, as one could have read
|
||||
* the current index but not have incremented the lock counter yet.
|
||||
*
|
||||
* Possible bug: There is no guarantee that there haven't been
|
||||
* ULONG_MAX increments of ->lock_count[] since the unlocks were
|
||||
* counted, meaning that this could return true even if there are
|
||||
* still active readers. Since there are no memory barriers around
|
||||
* srcu_flip(), the CPU is not required to increment ->completed
|
||||
* before running srcu_readers_unlock_idx(), which means that there
|
||||
* could be an arbitrarily large number of critical sections that
|
||||
* execute after srcu_readers_unlock_idx() but use the old value
|
||||
* of ->completed.
|
||||
*/
|
||||
return srcu_readers_lock_idx(sp, idx) == unlocks;
|
||||
}
|
||||
|
||||
/**
|
||||
* srcu_readers_active - returns true if there are readers. and false
|
||||
* otherwise
|
||||
* @sp: which srcu_struct to count active readers (holding srcu_read_lock).
|
||||
*
|
||||
* Note that this is not an atomic primitive, and can therefore suffer
|
||||
* severe errors when invoked on an active srcu_struct. That said, it
|
||||
* can be useful as an error check at cleanup time.
|
||||
*/
|
||||
static bool srcu_readers_active(struct srcu_struct *sp)
|
||||
{
|
||||
int cpu;
|
||||
unsigned long sum = 0;
|
||||
|
||||
for_each_possible_cpu(cpu) {
|
||||
struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu);
|
||||
|
||||
sum += READ_ONCE(cpuc->lock_count[0]);
|
||||
sum += READ_ONCE(cpuc->lock_count[1]);
|
||||
sum -= READ_ONCE(cpuc->unlock_count[0]);
|
||||
sum -= READ_ONCE(cpuc->unlock_count[1]);
|
||||
}
|
||||
return sum;
|
||||
}
|
||||
|
||||
#define SRCU_INTERVAL 1
|
||||
|
||||
/**
|
||||
* cleanup_srcu_struct - deconstruct a sleep-RCU structure
|
||||
* @sp: structure to clean up.
|
||||
*
|
||||
* Must invoke this after you are finished using a given srcu_struct that
|
||||
* was initialized via init_srcu_struct(), else you leak memory.
|
||||
*/
|
||||
void cleanup_srcu_struct(struct srcu_struct *sp)
|
||||
{
|
||||
WARN_ON_ONCE(atomic_read(&sp->srcu_exp_cnt));
|
||||
if (WARN_ON(srcu_readers_active(sp)))
|
||||
return; /* Leakage unless caller handles error. */
|
||||
if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist)))
|
||||
return; /* Leakage unless caller handles error. */
|
||||
flush_delayed_work(&sp->work);
|
||||
if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE)) {
|
||||
pr_info("cleanup_srcu_struct: Active srcu_struct %lu CBs %c state: %d\n", rcu_segcblist_n_cbs(&sp->srcu_cblist), ".E"[rcu_segcblist_empty(&sp->srcu_cblist)], rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
|
||||
return; /* Caller forgot to stop doing call_srcu()? */
|
||||
}
|
||||
free_percpu(sp->per_cpu_ref);
|
||||
sp->per_cpu_ref = NULL;
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
|
||||
|
||||
/*
|
||||
* Counts the new reader in the appropriate per-CPU element of the
|
||||
* srcu_struct. Must be called from process context.
|
||||
* Returns an index that must be passed to the matching srcu_read_unlock().
|
||||
*/
|
||||
int __srcu_read_lock(struct srcu_struct *sp)
|
||||
{
|
||||
int idx;
|
||||
|
||||
idx = READ_ONCE(sp->completed) & 0x1;
|
||||
__this_cpu_inc(sp->per_cpu_ref->lock_count[idx]);
|
||||
smp_mb(); /* B */ /* Avoid leaking the critical section. */
|
||||
return idx;
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(__srcu_read_lock);
|
||||
|
||||
/*
|
||||
* Removes the count for the old reader from the appropriate per-CPU
|
||||
* element of the srcu_struct. Note that this may well be a different
|
||||
* CPU than that which was incremented by the corresponding srcu_read_lock().
|
||||
* Must be called from process context.
|
||||
*/
|
||||
void __srcu_read_unlock(struct srcu_struct *sp, int idx)
|
||||
{
|
||||
smp_mb(); /* C */ /* Avoid leaking the critical section. */
|
||||
this_cpu_inc(sp->per_cpu_ref->unlock_count[idx]);
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(__srcu_read_unlock);
|
||||
|
||||
/*
|
||||
* We use an adaptive strategy for synchronize_srcu() and especially for
|
||||
* synchronize_srcu_expedited(). We spin for a fixed time period
|
||||
* (defined below) to allow SRCU readers to exit their read-side critical
|
||||
* sections. If there are still some readers after a few microseconds,
|
||||
* we repeatedly block for 1-millisecond time periods.
|
||||
*/
|
||||
#define SRCU_RETRY_CHECK_DELAY 5
|
||||
|
||||
/*
|
||||
* Start an SRCU grace period.
|
||||
*/
|
||||
static void srcu_gp_start(struct srcu_struct *sp)
|
||||
{
|
||||
int state;
|
||||
|
||||
rcu_segcblist_accelerate(&sp->srcu_cblist,
|
||||
rcu_seq_snap(&sp->srcu_gp_seq));
|
||||
rcu_seq_start(&sp->srcu_gp_seq);
|
||||
state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
|
||||
WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
|
||||
}
|
||||
|
||||
/*
|
||||
* Wait until all readers counted by array index idx complete, but
|
||||
* loop an additional time if there is an expedited grace period pending.
|
||||
* The caller must ensure that ->completed is not changed while checking.
|
||||
*/
|
||||
static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
|
||||
{
|
||||
for (;;) {
|
||||
if (srcu_readers_active_idx_check(sp, idx))
|
||||
return true;
|
||||
if (--trycount + !!atomic_read(&sp->srcu_exp_cnt) <= 0)
|
||||
return false;
|
||||
udelay(SRCU_RETRY_CHECK_DELAY);
|
||||
}
|
||||
}
|
||||
|
||||
/*
|
||||
* Increment the ->completed counter so that future SRCU readers will
|
||||
* use the other rank of the ->(un)lock_count[] arrays. This allows
|
||||
* us to wait for pre-existing readers in a starvation-free manner.
|
||||
*/
|
||||
static void srcu_flip(struct srcu_struct *sp)
|
||||
{
|
||||
WRITE_ONCE(sp->completed, sp->completed + 1);
|
||||
|
||||
/*
|
||||
* Ensure that if the updater misses an __srcu_read_unlock()
|
||||
* increment, that task's next __srcu_read_lock() will see the
|
||||
* above counter update. Note that both this memory barrier
|
||||
* and the one in srcu_readers_active_idx_check() provide the
|
||||
* guarantee for __srcu_read_lock().
|
||||
*/
|
||||
smp_mb(); /* D */ /* Pairs with C. */
|
||||
}
|
||||
|
||||
/*
|
||||
* End an SRCU grace period.
|
||||
*/
|
||||
static void srcu_gp_end(struct srcu_struct *sp)
|
||||
{
|
||||
rcu_seq_end(&sp->srcu_gp_seq);
|
||||
|
||||
spin_lock_irq(&sp->queue_lock);
|
||||
rcu_segcblist_advance(&sp->srcu_cblist,
|
||||
rcu_seq_current(&sp->srcu_gp_seq));
|
||||
spin_unlock_irq(&sp->queue_lock);
|
||||
}
|
||||
|
||||
/*
|
||||
* Enqueue an SRCU callback on the specified srcu_struct structure,
|
||||
* initiating grace-period processing if it is not already running.
|
||||
*
|
||||
* Note that all CPUs must agree that the grace period extended beyond
|
||||
* all pre-existing SRCU 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 corresponding SRCU read-side critical section whose beginning
|
||||
* preceded the call to call_rcu(). It also means that each CPU executing
|
||||
* an SRCU 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 SRCU 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 SRCU 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()".
|
||||
* This guarantee applies even if CPU A and CPU B are the same CPU (but
|
||||
* again only if the system has more than one CPU).
|
||||
*
|
||||
* Of course, these guarantees apply only for invocations of call_srcu(),
|
||||
* srcu_read_lock(), and srcu_read_unlock() that are all passed the same
|
||||
* srcu_struct structure.
|
||||
*/
|
||||
void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
|
||||
rcu_callback_t func)
|
||||
{
|
||||
unsigned long flags;
|
||||
|
||||
head->next = NULL;
|
||||
head->func = func;
|
||||
spin_lock_irqsave(&sp->queue_lock, flags);
|
||||
smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
|
||||
rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
|
||||
if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
|
||||
srcu_gp_start(sp);
|
||||
queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
|
||||
}
|
||||
spin_unlock_irqrestore(&sp->queue_lock, flags);
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(call_srcu);
|
||||
|
||||
static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);
|
||||
|
||||
/*
|
||||
* Helper function for synchronize_srcu() and synchronize_srcu_expedited().
|
||||
*/
|
||||
static void __synchronize_srcu(struct srcu_struct *sp)
|
||||
{
|
||||
struct rcu_synchronize rcu;
|
||||
struct rcu_head *head = &rcu.head;
|
||||
|
||||
RCU_LOCKDEP_WARN(lock_is_held(&sp->dep_map) ||
|
||||
lock_is_held(&rcu_bh_lock_map) ||
|
||||
lock_is_held(&rcu_lock_map) ||
|
||||
lock_is_held(&rcu_sched_lock_map),
|
||||
"Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
|
||||
|
||||
if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
|
||||
return;
|
||||
might_sleep();
|
||||
init_completion(&rcu.completion);
|
||||
|
||||
head->next = NULL;
|
||||
head->func = wakeme_after_rcu;
|
||||
spin_lock_irq(&sp->queue_lock);
|
||||
smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
|
||||
if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
|
||||
/* steal the processing owner */
|
||||
rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
|
||||
srcu_gp_start(sp);
|
||||
spin_unlock_irq(&sp->queue_lock);
|
||||
/* give the processing owner to work_struct */
|
||||
srcu_reschedule(sp, 0);
|
||||
} else {
|
||||
rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
|
||||
spin_unlock_irq(&sp->queue_lock);
|
||||
}
|
||||
|
||||
wait_for_completion(&rcu.completion);
|
||||
smp_mb(); /* Caller's later accesses after GP. */
|
||||
}
|
||||
|
||||
/**
|
||||
* synchronize_srcu_expedited - Brute-force SRCU grace period
|
||||
* @sp: srcu_struct with which to synchronize.
|
||||
*
|
||||
* Wait for an SRCU grace period to elapse, but be more aggressive about
|
||||
* spinning rather than blocking when waiting.
|
||||
*
|
||||
* Note that synchronize_srcu_expedited() has the same deadlock and
|
||||
* memory-ordering properties as does synchronize_srcu().
|
||||
*/
|
||||
void synchronize_srcu_expedited(struct srcu_struct *sp)
|
||||
{
|
||||
bool do_norm = rcu_gp_is_normal();
|
||||
|
||||
if (!do_norm) {
|
||||
atomic_inc(&sp->srcu_exp_cnt);
|
||||
smp_mb__after_atomic(); /* increment before GP. */
|
||||
}
|
||||
__synchronize_srcu(sp);
|
||||
if (!do_norm) {
|
||||
smp_mb__before_atomic(); /* GP before decrement. */
|
||||
atomic_dec(&sp->srcu_exp_cnt);
|
||||
}
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
|
||||
|
||||
/**
|
||||
* synchronize_srcu - wait for prior SRCU read-side critical-section completion
|
||||
* @sp: srcu_struct with which to synchronize.
|
||||
*
|
||||
* Wait for the count to drain to zero of both indexes. To avoid the
|
||||
* possible starvation of synchronize_srcu(), it waits for the count of
|
||||
* the index=((->completed & 1) ^ 1) to drain to zero at first,
|
||||
* and then flip the completed and wait for the count of the other index.
|
||||
*
|
||||
* Can block; must be called from process context.
|
||||
*
|
||||
* Note that it is illegal to call synchronize_srcu() from the corresponding
|
||||
* SRCU read-side critical section; doing so will result in deadlock.
|
||||
* However, it is perfectly legal to call synchronize_srcu() on one
|
||||
* srcu_struct from some other srcu_struct's read-side critical section,
|
||||
* as long as the resulting graph of srcu_structs is acyclic.
|
||||
*
|
||||
* There are memory-ordering constraints implied by synchronize_srcu().
|
||||
* On systems with more than one CPU, when synchronize_srcu() returns,
|
||||
* each CPU is guaranteed to have executed a full memory barrier since
|
||||
* the end of its last corresponding SRCU-sched read-side critical section
|
||||
* whose beginning preceded the call to synchronize_srcu(). In addition,
|
||||
* each CPU having an SRCU read-side critical section that extends beyond
|
||||
* the return from synchronize_srcu() is guaranteed to have executed a
|
||||
* full memory barrier after the beginning of synchronize_srcu() and before
|
||||
* the beginning of that SRCU 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 synchronize_srcu(), which returned
|
||||
* to its caller on CPU B, then both CPU A and CPU B are guaranteed
|
||||
* to have executed a full memory barrier during the execution of
|
||||
* synchronize_srcu(). This guarantee applies even if CPU A and CPU B
|
||||
* are the same CPU, but again only if the system has more than one CPU.
|
||||
*
|
||||
* Of course, these memory-ordering guarantees apply only when
|
||||
* synchronize_srcu(), srcu_read_lock(), and srcu_read_unlock() are
|
||||
* passed the same srcu_struct structure.
|
||||
*/
|
||||
void synchronize_srcu(struct srcu_struct *sp)
|
||||
{
|
||||
if (rcu_gp_is_expedited())
|
||||
synchronize_srcu_expedited(sp);
|
||||
else
|
||||
__synchronize_srcu(sp);
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(synchronize_srcu);
|
||||
|
||||
/**
|
||||
* srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
|
||||
* @sp: srcu_struct on which to wait for in-flight callbacks.
|
||||
*/
|
||||
void srcu_barrier(struct srcu_struct *sp)
|
||||
{
|
||||
synchronize_srcu(sp);
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(srcu_barrier);
|
||||
|
||||
/**
|
||||
* srcu_batches_completed - return batches completed.
|
||||
* @sp: srcu_struct on which to report batch completion.
|
||||
*
|
||||
* Report the number of batches, correlated with, but not necessarily
|
||||
* precisely the same as, the number of grace periods that have elapsed.
|
||||
*/
|
||||
unsigned long srcu_batches_completed(struct srcu_struct *sp)
|
||||
{
|
||||
return sp->completed;
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(srcu_batches_completed);
|
||||
|
||||
/*
|
||||
* Core SRCU state machine. Advance callbacks from ->batch_check0 to
|
||||
* ->batch_check1 and then to ->batch_done as readers drain.
|
||||
*/
|
||||
static void srcu_advance_batches(struct srcu_struct *sp)
|
||||
{
|
||||
int idx;
|
||||
|
||||
/*
|
||||
* Because readers might be delayed for an extended period after
|
||||
* fetching ->completed for their index, at any point in time there
|
||||
* might well be readers using both idx=0 and idx=1. We therefore
|
||||
* need to wait for readers to clear from both index values before
|
||||
* invoking a callback.
|
||||
*
|
||||
* The load-acquire ensures that we see the accesses performed
|
||||
* by the prior grace period.
|
||||
*/
|
||||
idx = rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq)); /* ^^^ */
|
||||
if (idx == SRCU_STATE_IDLE) {
|
||||
spin_lock_irq(&sp->queue_lock);
|
||||
if (rcu_segcblist_empty(&sp->srcu_cblist)) {
|
||||
spin_unlock_irq(&sp->queue_lock);
|
||||
return;
|
||||
}
|
||||
idx = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
|
||||
if (idx == SRCU_STATE_IDLE)
|
||||
srcu_gp_start(sp);
|
||||
spin_unlock_irq(&sp->queue_lock);
|
||||
if (idx != SRCU_STATE_IDLE)
|
||||
return; /* Someone else started the grace period. */
|
||||
}
|
||||
|
||||
if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
|
||||
idx = 1 ^ (sp->completed & 1);
|
||||
if (!try_check_zero(sp, idx, 1))
|
||||
return; /* readers present, retry later. */
|
||||
srcu_flip(sp);
|
||||
rcu_seq_set_state(&sp->srcu_gp_seq, SRCU_STATE_SCAN2);
|
||||
}
|
||||
|
||||
if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN2) {
|
||||
|
||||
/*
|
||||
* SRCU read-side critical sections are normally short,
|
||||
* so check at least twice in quick succession after a flip.
|
||||
*/
|
||||
idx = 1 ^ (sp->completed & 1);
|
||||
if (!try_check_zero(sp, idx, 2))
|
||||
return; /* readers present, retry after later. */
|
||||
srcu_gp_end(sp);
|
||||
}
|
||||
}
|
||||
|
||||
/*
|
||||
* Invoke a limited number of SRCU callbacks that have passed through
|
||||
* their grace period. If there are more to do, SRCU will reschedule
|
||||
* the workqueue. Note that needed memory barriers have been executed
|
||||
* in this task's context by srcu_readers_active_idx_check().
|
||||
*/
|
||||
static void srcu_invoke_callbacks(struct srcu_struct *sp)
|
||||
{
|
||||
struct rcu_cblist ready_cbs;
|
||||
struct rcu_head *rhp;
|
||||
|
||||
spin_lock_irq(&sp->queue_lock);
|
||||
if (!rcu_segcblist_ready_cbs(&sp->srcu_cblist)) {
|
||||
spin_unlock_irq(&sp->queue_lock);
|
||||
return;
|
||||
}
|
||||
rcu_cblist_init(&ready_cbs);
|
||||
rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs);
|
||||
spin_unlock_irq(&sp->queue_lock);
|
||||
rhp = rcu_cblist_dequeue(&ready_cbs);
|
||||
for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
|
||||
local_bh_disable();
|
||||
rhp->func(rhp);
|
||||
local_bh_enable();
|
||||
}
|
||||
spin_lock_irq(&sp->queue_lock);
|
||||
rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs);
|
||||
spin_unlock_irq(&sp->queue_lock);
|
||||
}
|
||||
|
||||
/*
|
||||
* Finished one round of SRCU grace period. Start another if there are
|
||||
* more SRCU callbacks queued, otherwise put SRCU into not-running state.
|
||||
*/
|
||||
static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
|
||||
{
|
||||
bool pending = true;
|
||||
int state;
|
||||
|
||||
if (rcu_segcblist_empty(&sp->srcu_cblist)) {
|
||||
spin_lock_irq(&sp->queue_lock);
|
||||
state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
|
||||
if (rcu_segcblist_empty(&sp->srcu_cblist) &&
|
||||
state == SRCU_STATE_IDLE)
|
||||
pending = false;
|
||||
spin_unlock_irq(&sp->queue_lock);
|
||||
}
|
||||
|
||||
if (pending)
|
||||
queue_delayed_work(system_power_efficient_wq, &sp->work, delay);
|
||||
}
|
||||
|
||||
/*
|
||||
* This is the work-queue function that handles SRCU grace periods.
|
||||
*/
|
||||
void process_srcu(struct work_struct *work)
|
||||
{
|
||||
struct srcu_struct *sp;
|
||||
|
||||
sp = container_of(work, struct srcu_struct, work.work);
|
||||
|
||||
srcu_advance_batches(sp);
|
||||
srcu_invoke_callbacks(sp);
|
||||
srcu_reschedule(sp, atomic_read(&sp->srcu_exp_cnt) ? 0 : SRCU_INTERVAL);
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(process_srcu);
|
||||
Загрузка…
Ссылка в новой задаче