linux-kernel - Re: [PATCH] shm: optimize exit

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Message-ID: <20110803193457.GA6734@albatros>
Date:	Wed, 3 Aug 2011 23:34:57 +0400
From:	Vasiliy Kulikov <segoon@...nwall.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Manuel Lauss <manuel.lauss@...glemail.com>,
	Richard Weinberger <richard@....at>,
	Marc Zyngier <marc.zyngier@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] shm: optimize exit_shm()

On Wed, Aug 03, 2011 at 21:21 +0200, Oleg Nesterov wrote:
> > we should check .in_use once again after
> > down_write().
> 
> Why?

https://lkml.org/lkml/2011/8/3/277

"No, as I said in the comment above, other task may be holding the mutex and
deleting the last shm segment.  So, current task will see in_use == 1
before down_write(), but == 0 after it."

"Should" == additional check might speed the things, so it worth checking.

-- 
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments
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