linux-kernel - Re: [PATCH v2 -mm -next] ipc,sem: fix lockdep false positive

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Message-ID: <5155962A.9070705@surriel.com>
Date:	Fri, 29 Mar 2013 09:24:58 -0400
From:	Rik van Riel <riel@...riel.com>
To:	Michel Lespinasse <walken@...gle.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	torvalds@...ux-foundation.org, davidlohr.bueso@...com,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	hhuang@...hat.com, jason.low2@...com, lwoodman@...hat.com,
	chegu_vinod@...com, Dave Jones <davej@...hat.com>,
	benisty.e@...il.com, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v2 -mm -next] ipc,sem: fix lockdep false positive

On 03/29/2013 09:08 AM, Michel Lespinasse wrote:

>> That is where I had it initially. I may have gotten too clever
>> and worked on keeping more accesses read-only. If you want, I
>> can move it back here and re-submit the patch :)
>
> I think I would prefer that - I feel having it upper serves little
> purpose, as you still need to check it here, so we might as well be
> optimistic and check it only here. Or maybe I've missed the benefit of
> having it earlier - I just don't see it.

OK, will do.

> It still makes it possible (though less likely) that each simple semop
> taking this path might make the next one take it too, though. So, I'm
> not sure how to balance that against the starvation possibility. I'll
> leave it up to you then :)

Lets optimistically assume that userland is using the semaphores
for synchronization. That rather limits the potential for starvation.

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