Messages in this thread Patch in this message | | | From | Zqiang <> | Subject | [PATCH v2] rcu: Add per-CPU rcuc task info to RCU CPU stall warnings | Date | Mon, 24 Jan 2022 18:36:37 +0800 |
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When the 'use_softirq' be set zero, all RCU_SOFTIRQ processing be moved to per-CPU rcuc kthreads, if the rcuc kthreads is being starved, quiescent state can not report in time. the RCU stall may be triggered. this commit adds a stack trace of this CPU and dump rcuc kthreads stack to help analyze what prevents rcuc kthreads from running.
Signed-off-by: Zqiang <qiang1.zhang@intel.com> --- v1->v2: Avoid print anything when CPU is offline or idle.
kernel/rcu/tree.c | 3 +++ kernel/rcu/tree.h | 1 + kernel/rcu/tree_plugin.h | 3 +++ kernel/rcu/tree_stall.h | 36 ++++++++++++++++++++++++++++++++++++ 4 files changed, 43 insertions(+)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index a4c25a6283b0..e3fc31a0f546 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2850,10 +2850,12 @@ static void rcu_cpu_kthread(unsigned int cpu) { unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status); char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work); + unsigned long *j = this_cpu_ptr(&rcu_data.rcuc_activity); int spincnt; trace_rcu_utilization(TPS("Start CPU kthread@rcu_run")); for (spincnt = 0; spincnt < 10; spincnt++) { + WRITE_ONCE(*j, jiffies); local_bh_disable(); *statusp = RCU_KTHREAD_RUNNING; local_irq_disable(); @@ -2874,6 +2876,7 @@ static void rcu_cpu_kthread(unsigned int cpu) schedule_timeout_idle(2); trace_rcu_utilization(TPS("End CPU kthread@rcu_yield")); *statusp = RCU_KTHREAD_WAITING; + WRITE_ONCE(*j, jiffies); } static struct smp_hotplug_thread rcu_cpu_thread_spec = { diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 486fc901bd08..4e0fdebb62e8 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -237,6 +237,7 @@ struct rcu_data { /* rcuc per-CPU kthread or NULL. */ unsigned int rcu_cpu_kthread_status; char rcu_cpu_has_work; + unsigned long rcuc_activity; /* 7) Diagnostic data, including RCU CPU stall warnings. */ unsigned int softirq_snap; /* Snapshot of softirq activity. */ diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index c5b45c2f68a1..327bbfd79cc6 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -996,12 +996,15 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck) */ static void rcu_cpu_kthread_setup(unsigned int cpu) { + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); #ifdef CONFIG_RCU_BOOST struct sched_param sp; sp.sched_priority = kthread_prio; sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); #endif /* #ifdef CONFIG_RCU_BOOST */ + + WRITE_ONCE(rdp->rcuc_activity, jiffies); } #ifdef CONFIG_RCU_BOOST diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 21bebf7c9030..739a2d87ea5e 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -379,6 +379,15 @@ static bool rcu_is_gp_kthread_starving(unsigned long *jp) return j > 2 * HZ; } +static bool rcu_is_rcuc_kthread_starving(struct rcu_data *rdp, unsigned long *jp) +{ + unsigned long j = jiffies - READ_ONCE(rdp->rcuc_activity); + + if (jp) + *jp = j; + return j > 2 * HZ; +} + /* * Print out diagnostic information for the specified stalled CPU. * @@ -430,6 +439,30 @@ static void print_cpu_stall_info(int cpu) falsepositive ? " (false positive?)" : ""); } +static void rcuc_kthread_dump(struct rcu_data *rdp) +{ + int cpu; + unsigned long j; + struct task_struct *rcuc = rdp->rcu_cpu_kthread_task; + + if (rcu_is_rcuc_kthread_starving(rdp, &j)) { + cpu = rcuc ? task_cpu(rcuc) : -1; + + if (rcuc) { + pr_err("%s kthread starved for %ld jiffies, stack dump:\n", + rcuc->comm, j); + sched_show_task(rcuc); + if (cpu >= 0) { + if (cpu_online(cpu) && !idle_cpu(cpu)) { + pr_err("Dump current CPU stack:\n"); + if (!trigger_single_cpu_backtrace(cpu)) + dump_cpu_task(cpu); + } + } + } + } +} + /* Complain about starvation of grace-period kthread. */ static void rcu_check_gp_kthread_starvation(void) { @@ -601,6 +634,9 @@ static void print_cpu_stall(unsigned long gps) rcu_check_gp_kthread_expired_fqs_timer(); rcu_check_gp_kthread_starvation(); + if (!use_softirq) + rcuc_kthread_dump(rdp); + rcu_dump_cpu_stacks(); raw_spin_lock_irqsave_rcu_node(rnp, flags); -- 2.25.1
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