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workqueue: Restrict affinity change to rescuer 

[ Upstream commit 640f17c824 ]

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>
This commit is contained in:
Peter Zijlstra 2021-01-15 19:08:36 +01:00 committed by Greg Kroah-Hartman
parent b20475a80b
commit b80df6517d
1 changed files with 3 additions and 6 deletions
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9
kernel/workqueue.c
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@ -1845,12 +1845,6 @@ 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
@ -1859,6 +1853,9 @@ 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;