From 577389423187d8b51dfe6199297e579a3419b72b Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 8 May 2018 14:18:57 -0700 Subject: [PATCH] rcu: Add CPU online/offline state to dump_blkd_tasks() Interactions between CPU-hotplug operations and grace-period initialization can result in dump_blkd_tasks(). One of the first debugging actions in this case is to search back in dmesg to work out which of the affected rcu_node structure's CPUs are online and to determine the last CPU-hotplug operation affecting any of those CPUs. This can be laborious and error-prone, especially when console output is lost. This commit therefore causes dump_blkd_tasks() to dump the state of the affected rcu_node structure's CPUs and the last grace period during which the last offline and online operation affected each of these CPUs. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 12 ++++++++++-- kernel/rcu/tree.h | 12 +++++++++--- kernel/rcu/tree_plugin.h | 25 ++++++++++++++++++++----- 3 files changed, 39 insertions(+), 10 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 5f1a11f1f7bc..a2503ef1bbe2 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1954,7 +1954,7 @@ static bool rcu_gp_init(struct rcu_state *rsp) rcu_gp_slow(rsp, gp_init_delay); raw_spin_lock_irqsave_rcu_node(rnp, flags); rdp = this_cpu_ptr(rsp->rda); - rcu_preempt_check_blocked_tasks(rnp); + rcu_preempt_check_blocked_tasks(rsp, rnp); rnp->qsmask = rnp->qsmaskinit; WRITE_ONCE(rnp->gp_seq, rsp->gp_seq); if (rnp == rdp->mynode) @@ -2063,7 +2063,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) rcu_for_each_node_breadth_first(rsp, rnp) { raw_spin_lock_irq_rcu_node(rnp); if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp))) - dump_blkd_tasks(rnp, 10); + dump_blkd_tasks(rsp, rnp, 10); WARN_ON_ONCE(rnp->qsmask); WRITE_ONCE(rnp->gp_seq, new_gp_seq); rdp = this_cpu_ptr(rsp->rda); @@ -3516,6 +3516,10 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp) rdp->dynticks = &per_cpu(rcu_dynticks, cpu); WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != 1); WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp->dynticks))); + rdp->rcu_ofl_gp_seq = rsp->gp_seq; + rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED; + rdp->rcu_onl_gp_seq = rsp->gp_seq; + rdp->rcu_onl_gp_flags = RCU_GP_CLEANED; rdp->cpu = cpu; rdp->rsp = rsp; rcu_boot_init_nocb_percpu_data(rdp); @@ -3711,6 +3715,8 @@ void rcu_cpu_starting(unsigned int cpu) /* Allow lockless access for expedited grace periods. */ smp_store_release(&rsp->ncpus, rsp->ncpus + nbits); /* ^^^ */ rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */ + rdp->rcu_onl_gp_seq = READ_ONCE(rsp->gp_seq); + rdp->rcu_onl_gp_flags = READ_ONCE(rsp->gp_flags); if (rnp->qsmask & mask) { /* RCU waiting on incoming CPU? */ /* Report QS -after- changing ->qsmaskinitnext! */ rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags); @@ -3738,6 +3744,8 @@ static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp) mask = rdp->grpmask; spin_lock(&rsp->ofl_lock); raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */ + rdp->rcu_ofl_gp_seq = READ_ONCE(rsp->gp_seq); + rdp->rcu_ofl_gp_flags = READ_ONCE(rsp->gp_flags); if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */ /* Report quiescent state -before- changing ->qsmaskinitnext! */ rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags); diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 795d469c6f67..f52bc059bfec 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -255,12 +255,16 @@ struct rcu_data { /* Leader CPU takes GP-end wakeups. */ #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ - /* 7) RCU CPU stall data. */ + /* 7) Diagnostic data, including RCU CPU stall warnings. */ unsigned int softirq_snap; /* Snapshot of softirq activity. */ /* ->rcu_iw* fields protected by leaf rcu_node ->lock. */ struct irq_work rcu_iw; /* Check for non-irq activity. */ bool rcu_iw_pending; /* Is ->rcu_iw pending? */ unsigned long rcu_iw_gp_seq; /* ->gp_seq associated with ->rcu_iw. */ + unsigned long rcu_ofl_gp_seq; /* ->gp_seq at last offline. */ + short rcu_ofl_gp_flags; /* ->gp_flags at last offline. */ + unsigned long rcu_onl_gp_seq; /* ->gp_seq at last online. */ + short rcu_onl_gp_flags; /* ->gp_flags at last online. */ int cpu; struct rcu_state *rsp; @@ -431,11 +435,13 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp); static void rcu_print_detail_task_stall(struct rcu_state *rsp); static int rcu_print_task_stall(struct rcu_node *rnp); static int rcu_print_task_exp_stall(struct rcu_node *rnp); -static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp); +static void rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, + struct rcu_node *rnp); static void rcu_preempt_check_callbacks(void); void call_rcu(struct rcu_head *head, rcu_callback_t func); static void __init __rcu_init_preempt(void); -static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck); +static void dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, + int ncheck); static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags); static void rcu_preempt_boost_start_gp(struct rcu_node *rnp); static void invoke_rcu_callbacks_kthread(void); diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index f45ff97b0d51..613372246a07 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -699,13 +699,14 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp) * 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) +static void +rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp) { struct task_struct *t; RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n"); if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp))) - dump_blkd_tasks(rnp, 10); + dump_blkd_tasks(rsp, rnp, 10); if (rcu_preempt_has_tasks(rnp) && (rnp->qsmaskinit || rnp->wait_blkd_tasks)) { rnp->gp_tasks = rnp->blkd_tasks.next; @@ -854,10 +855,14 @@ void exit_rcu(void) * Dump the blocked-tasks state, but limit the list dump to the * specified number of elements. */ -static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck) +static void +dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, int ncheck) { + int cpu; int i; struct list_head *lhp; + bool onl; + struct rcu_data *rdp; struct rcu_node *rnp1; raw_lockdep_assert_held_rcu_node(rnp); @@ -877,6 +882,14 @@ static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck) break; } pr_cont("\n"); + for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) { + rdp = per_cpu_ptr(rsp->rda, cpu); + onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp)); + pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n", + cpu, ".o"[onl], + (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags, + (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags); + } } #else /* #ifdef CONFIG_PREEMPT_RCU */ @@ -949,7 +962,8 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp) * 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) +static void +rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp) { WARN_ON_ONCE(rnp->qsmask); } @@ -990,7 +1004,8 @@ void exit_rcu(void) /* * Dump the guaranteed-empty blocked-tasks state. Trust but verify. */ -static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck) +static void +dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, int ncheck) { WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks)); }