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>
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 0695c78..1d99c52 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1846,12 +1846,6 @@
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
* definition for details.
@@ -1859,6 +1853,9 @@
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;