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Date: Wed, 3 Aug 2011 23:34:57 +0400
From: Vasiliy Kulikov <segoon@openwall.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Manuel Lauss <manuel.lauss@googlemail.com>,
        Richard Weinberger <richard@nod.at>,
        Marc Zyngier <marc.zyngier@arm.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] shm: optimize exit_shm()
Message-ID: <20110803193457.GA6734@albatros>
References: <20110803140456.GA14393@redhat.com>
 <20110803182417.GA2510@albatros>
 <20110803182826.GB2865@albatros>
 <20110803192138.GB31267@redhat.com>
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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