linux-kernel - Re: [PATCH, take4] FUTEX : new PRIVATE futexes

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Date:	Wed, 11 Apr 2007 17:22:57 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Eric Dumazet <dada1@...mosbay.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Jones <davej@...hat.com>,
	Ulrich Drepper <drepper@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...e.de>,
	Ravikiran G Thirumalai <kiran@...lex86.org>,
	"Shai Fultheim (Shai@...lex86.org)" <shai@...lex86.org>,
	pravin b shelar <pravin.shelar@...softinc.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH, take4] FUTEX : new PRIVATE futexes

Eric Dumazet wrote:
> On Sat, 07 Apr 2007 19:30:14 +1000
> Nick Piggin <nickpiggin@...oo.com.au> wrote:
> 
> 
>>Eric Dumazet wrote:
> 
>  
> 
>>>- Current mm code have a problem with 64bit futexes, as spoted by Nick :
>>>
>>>get_futex_key() does a check against sizeof(u32) regardless of futex being 64bits or not.
>>>So it is possible a 64bit futex spans two pages of memory...
>>>I had to change get_futex_key() prototype to be able to do a correct test.
>>
>>I wonder if it should be encfocing alignment to keep in on 1 page?
> 
> 
> I believe I just did that :)

Yes :P What I was trying to say before jumping on a plane is that
sys_futex/sys_futex64 calls should each check their own address alignment, so
the deeper parts of the call stack always know alignment is correct.

This will remove all the fsize you pass around, and also sanitise the userspace
argument much higher in the call stack, which is very preferable and more
conventional.

Maybe this isn't possible (it's very obvious, so there may be a good reason it
hasn't been done).

-- 
SUSE Labs, Novell Inc.
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