linux-kernel - Re: [PATCH] make cancel_rearming_delayed

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Message-ID: <20070515220812.GB615@tv-sign.ru>
Date:	Wed, 16 May 2007 02:08:12 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Jarek Poplawski <jarkao2@...pl>
Cc:	Tejun Heo <htejun@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Chinner <dgc@....com>,
	David Howells <dhowells@...hat.com>,
	Gautham Shenoy <ego@...ibm.com>, Ingo Molnar <mingo@...e.hu>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] make cancel_rearming_delayed_work() reliable

On 05/15, Jarek Poplawski wrote:
> 
> I've overheared somebody is talking about my favorite 2-nd bit!
> Probably I miss many points (your talk isn't the most clear),
> but I wonder if this bit couldn't be used otherwise: try_to_grab_
> sets the bit - others know cancel is pending, so don't disturb:
> e.g. insert_work doesn't queue (at least after works' cpu change,
> which seems to be the main problem here). Probably there is
> no reason to test this bit in all places - only in the most
> problematic; so, in insert_work maybe only after checking
> the cpu was changed. If this way is possible, we could avoid
> setting the VALID bit when not needed (no cancel pending). Maybe
> we could also think about some form of cooperation - e.g. clearing
> of this or other bit to ack the work was catched - of course
> this last thing could be too much, so not necessarily now.

We already discussed this... Surely, we can do this. I believe
this will complicate (and _imho_ uglify) the code too much.

May be I am wrong. Please provide a detailed description?

Oleg.

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