linux-kernel - Re: [PATCH V2] futex: Fix the write access fault problem for real

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Message-ID: <alpine.LFD.2.01.0906240946000.3240@localhost.localdomain>
Date:	Wed, 24 Jun 2009 09:46:59 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Darren Hart <dvhltc@...ibm.com>
Subject: Re: [PATCH V2] futex: Fix the write access fault problem for real



On Wed, 24 Jun 2009, Thomas Gleixner wrote:
> 
> The solution is to not rely on access_ok and get_user() for any write
> access related fault on private and shared futexes. Instead we need to
> fault it in with verification of write access.
> 
> There is no generic non destructive write mechanism which would fault
> the user page in trough a #PF, but as we already know that we will
> fault we can as well call get_user_pages() directly and avoid the #PF
> overhead.

Ack. Patch looks saner this way, and the commit message explains the 
issues.

		Linus
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