Re: [PATCH v3] workqueue: Fix double kfree for rescuer

From: Markus Elfring
Date: Mon May 25 2020 - 06:02:15 EST

> The callback function "rcu_free_wq" could be called after memory
> was released for "rescuer" already, Thus delete a misplaced call
> of the function "kfree".

I got into the mood to follow your interpretation of the
software situation for a moment.

I have taken another look also at the implementation of the function âdestroy_workqueueâ.

* The function call âkfree(rescuer)â can be performed there in an if branch
after the statement âwq->rescuer = NULLâ was executed.

* This data processing is independent from a possible call of the
function âcall_rcu(&wq->rcu, rcu_free_wq)â in another if branch.
Thus it seems that a null pointer is intentionally passed by a data structure
member to this callback function on demand.
The corresponding call of the function âkfreeâ can tolerate this special case.

Now I find that the proposed change can be inappropriate.
I'm sorry for undesirable confusion because of this patch review.