Re: + kthread-fix-kthread_mod_delayed_work-vs-kthread_cancel_delayed_work_sync-race.patch added to -mm tree

[Oleg Nesterov <oleg@redhat.com>]

On 05/24, Petr Mladek wrote:
>
> Your patch changes the semantic. The current semantic is the same for
> the workqueue's counter-part mod_delayed_work_on().

OK, I see, thanks. I was confused by the comment.

> We should actually keep the "ret" value as is to stay compatible with
> workqueue API:
>
> 	/*
> 	 * Canceling could run in parallel from kthread_cancel_delayed_work_sync
> 	 * and change work's canceling count as the spinlock is released and regain
> 	 * in __kthread_cancel_work so we need to check the count again. Otherwise,
> 	 * we might incorrectly queue the dwork and further cause
> 	 * cancel_delayed_work_sync thread waiting for flush dwork endlessly.
> 	 *
> 	 * Keep the ret code. The API primary informs the caller
> 	 * whether some pending work has been canceled (not proceed).
> 	 */
> 	if (work->canceling)
> 		goto out;

Agreed, we should keep the "ret" value.

but unless I am confused again this doesn't match mod_delayed_work_on()
which always returns true if it races with cancel(). Nevermind, I think
this doesn't matter.

Thanks,

Oleg.