linux-kernel - Re: [PATCH, v3] shmat: introduce flag SHM_MAP_NOT

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Message-ID: <20081008112037.6fa37c0b@lxorguk.ukuu.org.uk>
Date:	Wed, 8 Oct 2008 11:20:37 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Ingo Molnar <mingo@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Hugh Dickins <hugh@...itas.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH, v3] shmat: introduce flag SHM_MAP_NOT_FIXED

> That is racy when multi threaded because shmat() doesn't replace, so you 
> would need to munmap() inbetween and someone else could steal the area
> then. Yes you could stick a loop around it. It could livelock.
> No, it's not a good interface I would advocate.

You could just use pthread mutexes in your application. The rôle of the
kernel is not to provide nappies for people who think programming is too
hard but to provide services that can be used to build applications.

Alan
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