From: Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp>
To: Andi Kleen <andi@firstfloor.org>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [RESEND] [PATCH] VFS: make file->f_pos access atomic on 32bit arch
Date: Tue, 07 Oct 2008 19:11:26 +0900 [thread overview]
Message-ID: <6.0.0.20.2.20081007183452.0f052210@172.19.0.2> (raw)
In-Reply-To: <87hc7onbvo.fsf@basil.nowhere.org>
At 15:43 08/10/07, Andi Kleen wrote:
>Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp> writes:
>
>> Hi Andrew.
>>
>> Currently reading or writing file->f_pos is not atomic on 32bit environment,
>> so two or more simultaneous access can corrupt file->f_pos value.
>> There are some past discussions about this issue, but this is not fixed yet.
>> http://marc.info/?l=linux-kernel&m=120764199819899&w=2
>> http://marc.info/?l=linux-kernel&m=114490379102476&w=2
>
>Have you benchmarked if cmpxchg is cheaper than the seqlock? It's not
>clear to me a seqlock is really the right locking primitive for
>this. Normally seqlocks should be used when reading is much more
>frequent than writing, but it's doubtful that this is actually the
>case for f_pos.
Maybe cmpxchg8b is good for i486 or later x86, but i386 or other architectures
that do not have similar instruction needs some locking primitive. I think lazy
seqlock is one option for making file->f_pos access atomic.
next prev parent reply other threads:[~2008-10-07 10:14 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-10-07 5:07 Hisashi Hifumi
2008-10-07 6:43 ` Andi Kleen
2008-10-07 10:11 ` Hisashi Hifumi [this message]
2008-10-07 10:29 ` Andi Kleen
2008-10-07 16:27 ` Nick Piggin
2008-10-07 17:50 ` Andrew Morton
2008-10-07 18:59 ` Peter Zijlstra
2008-10-08 2:35 ` Nick Piggin
2008-10-08 2:52 ` Matthew Wilcox
2008-10-09 12:23 ` Pavel Machek
2008-10-09 12:49 ` Valdis.Kletnieks
2008-10-09 13:01 ` Matthew Wilcox
2008-10-09 13:38 ` Miklos Szeredi
2008-10-09 14:58 ` Linus Torvalds
2008-10-09 17:29 ` Jeremy Fitzhardinge
2008-10-08 4:48 ` Hisashi Hifumi
2008-10-08 5:10 ` Nick Piggin
2008-10-08 5:16 ` Matthew Wilcox
2008-10-08 6:28 ` Andrew Morton
2008-10-08 6:51 ` Peter Zijlstra
2008-10-08 8:32 ` Eric Dumazet
2008-10-08 8:48 ` Nick Piggin
2008-10-08 9:17 ` Peter Zijlstra
2008-10-09 21:51 ` dcg
2008-10-10 2:25 ` Nick Piggin
2008-10-09 12:16 ` Pavel Machek
2008-10-08 0:40 ` Nick Piggin
2008-10-07 18:00 ` Matthew Wilcox
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