[PATCH wq/for-6.9 v4 3/4] kernel/workqueue: Let rescuers follow unbound wq cpumask changes

Waiman Long
2024-02-07T01:19:39Z

From: Juri Lelli <juri.lelli@redhat.com>

When workqueue cpumask changes are committed the associated rescuer (if
one exists) affinity is not touched and this might be a problem down the
line for isolated setups.

Make sure rescuers affinity is updated every time a workqueue cpumask
changes, so that rescuers can't break isolation.

[longman: set_cpus_allowed_ptr() will block until the designated task
is enqueued on an allowed CPU, no wake_up_process() needed. Also use
the unbound_effective_cpumask() helper as suggested by Tejun.]

Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/workqueue.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 49fe082fe328..3044ad6f9496 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -5084,6 +5084,11 @@ static void apply_wqattrs_commit(struct apply_wqattrs_ctx *ctx)
/* update node_nr_active->max */
wq_update_node_max_active(ctx->wq, -1);

+ /* rescuer needs to respect wq cpumask changes */
+ if (ctx->wq->rescuer)
+ set_cpus_allowed_ptr(ctx->wq->rescuer->task,
+ unbound_effective_cpumask(ctx->wq));
+
mutex_unlock(&ctx->wq->mutex);
}

--
2.39.3