The patch below does not apply to the 5.13-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 868ad33bfa3bf39960982682ad3a0f8ebda1656e Mon Sep 17 00:00:00 2001

From: Thomas Gleixner tglx@linutronix.de Date: Sat, 28 Aug 2021 15:55:52 +0200 Subject: [PATCH] sched: Prevent balance_push() on remote runqueues

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 bigeasy@linutronix.de Signed-off-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/87zgt1hdw7.ffs@tglx

diff --git a/kernel/sched/core.c b/kernel/sched/core.c index f3b27c6c5153..b21a1857b75a 100644 --- 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;

/*