From: Jeff Moyer <jmoyer@redhat.com>
To: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: Jan Kara <jack@suse.cz>, Michael Kerrisk <mtk.manpages@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-man@vger.kernel.org, linux-mm@kvack.org, mgorman@suse.de,
npiggin@gmail.com
Subject: Re: [PATCH] Describe race of direct read and fork for unaligned buffers
Date: Tue, 01 May 2012 11:11:26 -0400 [thread overview]
Message-ID: <x49ehr4lyw1.fsf@segfault.boston.devel.redhat.com> (raw)
In-Reply-To: <CAHGf_=ojhwPUWJR0r+jVgjNd5h_sRrppzJntSpHzxyv+OuBueg@mail.gmail.com> (KOSAKI Motohiro's message of "Tue, 1 May 2012 10:37:20 -0400")
KOSAKI Motohiro <kosaki.motohiro@gmail.com> writes:
>> Hello,
>>
>> Thank you revisit this. But as far as my remember is correct, this issue is NOT
>> unaligned access issue. It's just get_user_pages(_fast) vs fork race issue. i.e.
>> DIRECT_IO w/ multi thread process should not use fork().
>
> The problem is, fork (and its COW logic) assume new access makes cow break,
> But page table protection can't detect a DMA write. Therefore DIO may override
> shared page data.
Hm, I've only seen this with misaligned or multiple sub-page-sized reads
in the same page. AFAIR, aligned, page-sized I/O does not get split.
But, I could be wrong...
Cheers,
Jeff
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next prev parent reply other threads:[~2012-05-01 15:20 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-30 9:30 [PATCH] Describe race of direct read and fork for unaligned buffers Jan Kara
2012-04-30 13:41 ` Jeff Moyer
2012-04-30 14:30 ` Mel Gorman
2012-05-01 5:50 ` Michael Kerrisk (man-pages)
2012-05-01 6:49 ` Nick Piggin
2012-05-01 14:31 ` KOSAKI Motohiro
2012-05-01 14:37 ` KOSAKI Motohiro
2012-05-01 15:11 ` Jeff Moyer [this message]
2012-05-01 15:34 ` KOSAKI Motohiro
2012-05-01 15:38 ` Jeff Moyer
2012-05-01 15:50 ` Nick Piggin
2012-05-01 23:51 ` Andrea Arcangeli
2012-05-02 8:17 ` Jan Kara
2012-05-02 9:09 ` Nick Piggin
2012-05-02 9:18 ` Jan Kara
2012-05-02 19:14 ` KOSAKI Motohiro
2012-05-02 19:23 ` Jan Kara
2012-05-02 19:25 ` KOSAKI Motohiro
2012-05-05 11:28 ` Michael Kerrisk (man-pages)
2012-05-05 15:29 ` KOSAKI Motohiro
2012-05-08 23:10 ` Nick Piggin
2012-05-09 5:35 ` Michael Kerrisk (man-pages)
2012-05-09 7:01 ` Nick Piggin
2012-05-09 7:18 ` Michael Kerrisk (man-pages)
2012-05-10 15:00 ` Jan Kara
2012-05-01 16:15 ` KOSAKI Motohiro
2012-05-01 17:56 ` Michael Kerrisk (man-pages)
2012-05-02 0:34 ` Nick Piggin
2012-05-02 3:04 ` Hugh Dickins
2012-05-02 3:10 ` Nick Piggin
2012-05-02 9:20 ` Jan Kara
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