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

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Message-ID: <20110803193906.GA2921@redhat.com>
Date:	Wed, 3 Aug 2011 21:39:06 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Vasiliy Kulikov <segoon@...nwall.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 08/03, Vasiliy Kulikov wrote:
>
> 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.

This is obvious,

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

and this is not.

I was confused, the changelog looks as if we _have to_ recheck
or something bad can happen.

But as I said, the patch looks correct anyway. I am not
sure the 2nd optimization really makes sense (this is very
unlikely case) but it doesn't hurt.

Oleg.

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