From: Thomas Gleixner Subject: sched: Prevent balance_push() on remote runqueues Date: Sat, 28 Aug 2021 15:55:52 +0200 sched_setscheduler() and rt_mutex_setprio() invoke the run-queue balance callback after changing priorities or the scheduling class of a task. The run-queue for which the callback is invoked can be local or remote. That's not a problem for the regular rq::push_work which is serialized with a busy flag in the run-queue struct, but for the balance_push() work which is only valid to be invoked on the outgoing CPU that's wrong. It not only triggers the debug warning, but also leaves the per CPU variable push_work unprotected, which can result in double enqueues on the stop machine list. Remove the warning and validate that the function is invoked on the outgoing CPU. Fixes: ae7927023243 ("sched: Optimize finish_lock_switch()") Reported-by: Sebastian Siewior Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org Cc: Juri Lelli Cc: Vincent Guittot Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Ben Segall Cc: Ingo Molnar Cc: Mel Gorman Cc: Daniel Bristot de Oliveira Cc: Dietmar Eggemann Signed-off-by: Sebastian Andrzej Siewior Link: https://lore.kernel.org/r/87zgt1hdw7.ffs@tglx --- V2: Use the correct check for the outgoing CPU --- kernel/sched/core.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -8523,7 +8523,6 @@ static void balance_push(struct rq *rq) struct task_struct *push_task = rq->curr; lockdep_assert_rq_held(rq); - SCHED_WARN_ON(rq->cpu != smp_processor_id()); /* * Ensure the thing is persistent until balance_push_set(.on = false); @@ -8531,9 +8530,10 @@ static void balance_push(struct rq *rq) rq->balance_callback = &balance_push_callback; /* - * Only active while going offline. + * Only active while going offline and when invoked on the outgoing + * CPU. */ - if (!cpu_dying(rq->cpu)) + if (!cpu_dying(rq->cpu) || rq != this_rq()) return; /*