linux-kernel - Re: [PATCH 25/25] ipc: don't use [delayed_]work

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Message-ID: <20121224194101.GC5344@liondog.tnic>
Date:	Mon, 24 Dec 2012 20:41:01 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Tejun Heo <tj@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 25/25] ipc: don't use [delayed_]work_pending()

On Mon, Dec 24, 2012 at 10:45:20AM -0800, Tejun Heo wrote:
> I was confused a bit there. We can't. Nothing guarantees that the
> queuer sees the cleared PENDING before the work item starts execution,
> and I think ipc memory hotplug could also be broken from that.

Stupid question: why not clear PENDING after execution is done? I'm
looking at process_one_work() here.

> It's highly unlikely to actually happen and there may be external
> locking which prevents the race from actually happening, but there's
> nothing synchronizing queueing and the execution of the work item.
> Looking at that part of code only, it's possible that it fails to
> queue the work item after a memory hotplug event even though the
> previous queueing already started execution and processed a couple
> notifiers.

Maybe failure to queue could be signalled with a proper return value
from __queue_work()?

Btw, I'm afraid I don't understand the "memory hotplug event" aspect and
how that can influence the queueing - all it does it is list_add_tail,
basically.

Thanks.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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