Patch "workqueue: Put the pwq after detaching the rescuer from the pool" has been added to the 6.13-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    workqueue: Put the pwq after detaching the rescuer from the pool

to the 6.13-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     workqueue-put-the-pwq-after-detaching-the-rescuer-fr.patch
and it can be found in the queue-6.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 9ebdb9b44fa33ac958fbec8d9835a05a2105da86
Author: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>
Date:   Thu Jan 23 16:25:35 2025 +0800

    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 <zzqq0103.hey@xxxxxxxxx>
    Cc: cheung wall <zzqq0103.hey@xxxxxxxxx>
    Link: https://lore.kernel.org/lkml/CAKHoSAvP3iQW+GwmKzWjEAOoPvzeWeoMO0Gz7Pp3_4kxt-RMoA@xxxxxxxxxxxxxx/
    Fixes: 68f83057b913("workqueue: Reap workers via kthread_stop() and remove detach_completion")
    Signed-off-by: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>
    Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 9362484a653c4..218f8c1388086 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3516,12 +3516,6 @@ static int rescuer_thread(void *__rescuer)
 			}
 		}
 
-		/*
-		 * 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.
@@ -3532,6 +3526,12 @@ static int rescuer_thread(void *__rescuer)
 
 		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);
 	}