From 36c6e17bf16922935a5a0dd073d5b032d34aa73d Mon Sep 17 00:00:00 2001 From: Valentin Schneider Date: Wed, 13 Jan 2021 18:31:41 +0000 Subject: [PATCH] sched/core: Print out straggler tasks in sched_cpu_dying() Since commit 1cf12e08bc4d ("sched/hotplug: Consolidate task migration on CPU unplug") tasks are expected to move themselves out of a out-going CPU. For most tasks this will be done automagically via BALANCE_PUSH, but percpu kthreads will have to cooperate and move themselves away one way or another. Currently, some percpu kthreads (workqueues being a notable exemple) do not cooperate nicely and can end up on an out-going CPU at the time sched_cpu_dying() is invoked. Print the dying rq's tasks to shed some light on the stragglers. Signed-off-by: Valentin Schneider Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Valentin Schneider Tested-by: Valentin Schneider Link: https://lkml.kernel.org/r/20210113183141.11974-1-valentin.schneider@arm.com --- kernel/sched/core.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 15d2562..627534f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7574,6 +7574,25 @@ static void calc_load_migrate(struct rq *rq) atomic_long_add(delta, &calc_load_tasks); } +static void dump_rq_tasks(struct rq *rq, const char *loglvl) +{ + struct task_struct *g, *p; + int cpu = cpu_of(rq); + + lockdep_assert_held(&rq->lock); + + printk("%sCPU%d enqueued tasks (%u total):\n", loglvl, cpu, rq->nr_running); + for_each_process_thread(g, p) { + if (task_cpu(p) != cpu) + continue; + + if (!task_on_rq_queued(p)) + continue; + + printk("%s\tpid: %d, name: %s\n", loglvl, p->pid, p->comm); + } +} + int sched_cpu_dying(unsigned int cpu) { struct rq *rq = cpu_rq(cpu); @@ -7583,7 +7602,10 @@ int sched_cpu_dying(unsigned int cpu) sched_tick_stop(cpu); rq_lock_irqsave(rq, &rf); - BUG_ON(rq->nr_running != 1 || rq_has_pinned_tasks(rq)); + if (rq->nr_running != 1 || rq_has_pinned_tasks(rq)) { + WARN(true, "Dying CPU not properly vacated!"); + dump_rq_tasks(rq, KERN_WARNING); + } rq_unlock_irqrestore(rq, &rf); calc_load_migrate(rq); -- 2.7.4