From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: mtk.manpages@gmail.com, lkml <linux-kernel@vger.kernel.org>,
Miklos Szeredi <miklos@szeredi.hu>,
"Theodore T'so" <tytso@mit.edu>, Christoph Hellwig <hch@lst.de>,
Chris Mason <clm@fb.com>, Dave Chinner <david@fromorbit.com>,
Linux-Fsdevel <linux-fsdevel@vger.kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
"J. Bruce Fields" <bfields@citi.umich.edu>,
Yongzhi Pan <panyongzhi@gmail.com>
Subject: Re: Update of file offset on write() etc. is non-atomic with I/O
Date: Thu, 06 Mar 2014 16:03:44 +0100 [thread overview]
Message-ID: <53188E50.70808@gmail.com> (raw)
In-Reply-To: <CA+55aFy4GvpFcboBiKdreU_Zh1RzynPoLxhvC9hijn60hkEZ3g@mail.gmail.com>
On 03/03/2014 06:36 PM, Linus Torvalds wrote:
> Ok, sorry for the long delay, I was distracted (and hoping that Al
> would come up with a patch).
>
> Anyway, attached is the patch I think we should do for this issue. It
> is fairly simple:
>
> - it adds a "f_pos_mutex" to the "struct file".
>
> - it adds a new FMODE_ATOMIC_POS flag to the file mode flags to mark
> things that need atomic f_pos updates
>
> - it makes the "struct fd" flags be two flags rather than one: the
> second flag is for "unlock f_pos_mutex when done"
>
> - it introduces "fd[get,put]_pos()" which gets the f_pos_mutex when required
>
> - it makes read/write/lseek use that.
>
> It's pretty damn straightforward, I think, and is minimally serializing.
>
> Al, comments? Yongzhi Pan, this is pretty much untested, but it's
> pretty simple and it does fix your test-case.
The original code (where Yongzhi Pan reported an issue) and
the multi_writer.c test code where both mine actually. Anyway,
I applied the patch to 3.14-rc5, and I (not withstanding the other
points raised by Al about the patch) I confirm that this patch makes
the problem that I'm seeing go away.
Thanks for looking at this, Linus.
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
next prev parent reply other threads:[~2014-03-06 15:04 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-17 15:41 Update of file offset on write() etc. is non-atomic with I/O Michael Kerrisk (man-pages)
2014-02-18 13:00 ` Michael Kerrisk
2014-02-20 17:14 ` Linus Torvalds
2014-03-03 17:36 ` Linus Torvalds
2014-03-03 21:45 ` Al Viro
2014-03-03 21:56 ` Linus Torvalds
2014-03-03 22:09 ` Al Viro
2014-03-03 22:20 ` Linus Torvalds
2014-03-03 22:01 ` Linus Torvalds
2014-03-03 22:10 ` Al Viro
2014-03-03 22:22 ` Linus Torvalds
2014-03-06 15:03 ` Michael Kerrisk (man-pages) [this message]
2014-03-07 3:38 ` Yongzhi Pan
[not found] <a8df285f-de7f-4a3a-9a19-e0ad07ab3a5c@blur>
2014-02-20 18:15 ` Zuckerman, Boris
2014-02-20 18:29 ` Al Viro
2014-02-21 6:01 ` Michael Kerrisk (man-pages)
2014-02-23 1:18 ` Kevin Easton
2014-02-23 7:38 ` Michael Kerrisk (man-pages)
2014-03-03 21:03 George Spelvin
2014-03-03 21:26 ` Al Viro
2014-03-03 21:52 ` Linus Torvalds
2014-03-03 22:01 ` Al Viro
2014-03-03 22:17 ` Linus Torvalds
2014-03-03 23:28 ` Al Viro
2014-03-03 23:34 ` Linus Torvalds
2014-03-03 23:42 ` Al Viro
2014-03-03 23:59 ` Linus Torvalds
2014-03-04 0:23 ` Al Viro
2014-03-04 0:42 ` Linus Torvalds
2014-03-04 1:05 ` Al Viro
2014-03-04 20:00 ` Al Viro
2014-03-04 21:17 ` Linus Torvalds
2014-03-05 0:04 ` Al Viro
2014-03-10 15:55 ` Al Viro
2014-03-03 22:55 ` Linus Torvalds
2014-03-03 23:23 ` Linus Torvalds
2014-03-03 23:39 ` Al Viro
2014-03-03 23:54 ` Linus Torvalds
2014-03-03 23:54 ` Al Viro
2014-03-04 20:11 ` Cedric Blancher
2014-03-04 0:07 ` George Spelvin
2014-05-04 7:04 ` Michael Kerrisk
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