Commit 1746d1dc authored Jan 15, 2021 by Peter Zijlstra Committed by Greg Kroah-Hartman Feb 07, 2021

workqueue: Restrict affinity change to rescuer



[ Upstream commit 640f17c82460e9724fd256f0a1f5d99e7ff0bda4 ]

create_worker() will already set the right affinity using
kthread_bind_mask(), this means only the rescuer will need to change
it's affinity.

Howveer, while in cpu-hot-unplug a regular task is not allowed to run
on online&&!active as it would be pushed away quite agressively. We
need KTHREAD_IS_PER_CPU to survive in that environment.

Therefore set the affinity after getting that magic flag.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Tested-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lkml.kernel.org/r/20210121103506.826629830@infradead.org


Signed-off-by: Sasha Levin <sashal@kernel.org>

parent fbad3218

kernel/workqueue.c

+3 −6

Original line number	Diff line number	Diff line
		@@ -1728,12 +1728,6 @@ static void worker_attach_to_pool(struct worker *worker,
		{
		mutex_lock(&wq_pool_attach_mutex);

		/*
		* set_cpus_allowed_ptr() will fail if the cpumask doesn't have any
		* online CPUs. It'll be re-applied when any of the CPUs come up.
		*/
		set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);

		/*
		* The wq_pool_attach_mutex ensures %POOL_DISASSOCIATED remains
		* stable across this function. See the comments above the flag
		@@ -1742,6 +1736,9 @@ static void worker_attach_to_pool(struct worker *worker,
		if (pool->flags & POOL_DISASSOCIATED)
		worker->flags \|= WORKER_UNBOUND;

		if (worker->rescue_wq)
		set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);

		list_add_tail(&worker->node, &pool->workers);
		worker->pool = pool;