linux-kernel - Re: [RFC PATCH 1/6] task_work: Provide means to check if a work is queued

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Date: Tue, 25 Jun 2024 17:16:25 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH 1/6] task_work: Provide means to check if a work is
 queued

And probably task_work_add() should do the same when it returns -ESRCH.

On 06/25, Oleg Nesterov wrote:
>
> On 06/25, Frederic Weisbecker wrote:
> >
> > --- a/kernel/task_work.c
> > +++ b/kernel/task_work.c
> > @@ -177,6 +177,7 @@ void task_work_run(void)
> >
> >  		do {
> >  			next = work->next;
> > +			work->next = TASK_WORK_DEQUEUED;
>
> OK, but then the additional change below makes sense too?
>
> Oleg.
> ---
>
> --- x/kernel/task_work.c
> +++ x/kernel/task_work.c
> @@ -106,8 +106,10 @@ task_work_cancel_match(struct task_struc
>  		if (!match(work, data)) {
>  			pprev = &work->next;
>  			work = READ_ONCE(*pprev);
> -		} else if (try_cmpxchg(pprev, &work, work->next))
> +		} else if (try_cmpxchg(pprev, &work, work->next)) {
> +			work->next = TASK_WORK_DEQUEUED;
>  			break;
> +		}
>  	}
>  	raw_spin_unlock_irqrestore(&task->pi_lock, flags);
>