linux-kernel - Re: [PATCH 7/9] PM: Add suspend blocking work.

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Message-ID: <20100426140603.GA5702@redhat.com>
Date:	Mon, 26 Apr 2010 16:06:03 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Arve Hjønnevåg <arve@...roid.com>
Cc:	Tejun Heo <tj@...nel.org>, linux-pm@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dmitri Vorobiev <dmitri.vorobiev@...ial.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 7/9] PM: Add suspend blocking work.

On 04/23, Arve Hjønnevåg wrote:
>
> On Fri, Apr 23, 2010 at 5:20 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>
> > The unblock code in run_workqueue() is racy,
> > it can unblock after the work was queued on another CPU, cwq->lock can't
> > help.
>
> If the work is both queued and starts running on another workqueue
> between "get_wq_data(work) == cwq" and "!work_pending(work)", then
> suspend_unblock will be called when it shouldn't. It should work fine
> if I change to it check pending first though, since it cannot move
> back to the current workqueue without locking cwq->lock first.

It can be queued on the same or different workqueue on another CPU,
right before run_workqueue() does unblock.

But I guess this doesn't matter. You already discussed this all with
Tejun while I was sleeping ;) And I agree very much, the new plan looks
much better imho.

Oleg.

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