From: Lai Jiangshan Date: Thu, 23 Jan 2025 08:25:35 +0000 (+0800) Subject: workqueue: Put the pwq after detaching the rescuer from the pool X-Git-Tag: v6.12.16~193 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e7c16028a424dd35be1064a68fa318be4359310f;p=thirdparty%2Fkernel%2Fstable.git workqueue: Put the pwq after detaching the rescuer from the pool [ Upstream commit e76946110137703c16423baf6ee177b751a34b7e ] The commit 68f83057b913("workqueue: Reap workers via kthread_stop() and remove detach_completion") adds code to reap the normal workers but mistakenly does not handle the rescuer and also removes the code waiting for the rescuer in put_unbound_pool(), which caused a use-after-free bug reported by Cheung Wall. To avoid the use-after-free bug, the pool’s reference must be held until the detachment is complete. Therefore, move the code that puts the pwq after detaching the rescuer from the pool. Reported-by: cheung wall Cc: cheung wall Link: https://lore.kernel.org/lkml/CAKHoSAvP3iQW+GwmKzWjEAOoPvzeWeoMO0Gz7Pp3_4kxt-RMoA@mail.gmail.com/ Fixes: 68f83057b913("workqueue: Reap workers via kthread_stop() and remove detach_completion") Signed-off-by: Lai Jiangshan Signed-off-by: Tejun Heo Signed-off-by: Sasha Levin --- diff --git a/kernel/workqueue.c b/kernel/workqueue.c index cee65cb431081..a9d64e08dffc7 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -3509,12 +3509,6 @@ repeat: } } - /* - * Put the reference grabbed by send_mayday(). @pool won't - * go away while we're still attached to it. - */ - put_pwq(pwq); - /* * Leave this pool. Notify regular workers; otherwise, we end up * with 0 concurrency and stalling the execution. @@ -3525,6 +3519,12 @@ repeat: worker_detach_from_pool(rescuer); + /* + * Put the reference grabbed by send_mayday(). @pool might + * go away any time after it. + */ + put_pwq_unlocked(pwq); + raw_spin_lock_irq(&wq_mayday_lock); }