From: "J. Bruce Fields" <bfields@fieldses.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [git pull] vfs and fs fixes
Date: Tue, 17 Apr 2012 13:06:14 -0400 [thread overview]
Message-ID: <20120417170614.GA29994@fieldses.org> (raw)
In-Reply-To: <CA+55aFzTKt43-qm4se2ac24kEVQO=aH8sckh0e-Lf-wydnYHfg@mail.gmail.com>
On Tue, Apr 17, 2012 at 09:33:06AM -0700, Linus Torvalds wrote:
> On Tue, Apr 17, 2012 at 9:22 AM, J. Bruce Fields <bfields@fieldses.org> wrote:
> >
> > Ugh, no, I think you're right:
> >
> > rename A/a->A/b
> > rename B/b->B/b
> >
> > where A/a and B/a are the same file, and A/b and B/b are the same file,
> > can result in the first rename holding the lock on A and a and waiting
> > on b, and the second holding the lock on B and b and waiting on a.
>
> In fact I don't think you need even that much. Just a simple
>
> touch a
> ln a b
> mv a b
>
> looks like it should deadlock on itself, no? source and dest inodes
> will be the same, so the mutex_lock() will just deadlock without even
> any ABBA race.
>
> (I didn't really check - maybe there is some reason that doesn't happen).
Yeah, rename has that funny exception that makes the above a no-op, so I
think that's safe.
But the patch is still wrong; back to the drawing board.
Maybe a paper bag over my head will help my concentration....
--b.
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WARNING: multiple messages have this Message-ID (diff)
From: "J. Bruce Fields" <bfields@fieldses.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [git pull] vfs and fs fixes
Date: Tue, 17 Apr 2012 13:06:14 -0400 [thread overview]
Message-ID: <20120417170614.GA29994@fieldses.org> (raw)
In-Reply-To: <CA+55aFzTKt43-qm4se2ac24kEVQO=aH8sckh0e-Lf-wydnYHfg@mail.gmail.com>
On Tue, Apr 17, 2012 at 09:33:06AM -0700, Linus Torvalds wrote:
> On Tue, Apr 17, 2012 at 9:22 AM, J. Bruce Fields <bfields@fieldses.org> wrote:
> >
> > Ugh, no, I think you're right:
> >
> > rename A/a->A/b
> > rename B/b->B/b
> >
> > where A/a and B/a are the same file, and A/b and B/b are the same file,
> > can result in the first rename holding the lock on A and a and waiting
> > on b, and the second holding the lock on B and b and waiting on a.
>
> In fact I don't think you need even that much. Just a simple
>
> touch a
> ln a b
> mv a b
>
> looks like it should deadlock on itself, no? source and dest inodes
> will be the same, so the mutex_lock() will just deadlock without even
> any ABBA race.
>
> (I didn't really check - maybe there is some reason that doesn't happen).
Yeah, rename has that funny exception that makes the above a no-op, so I
think that's safe.
But the patch is still wrong; back to the drawing board.
Maybe a paper bag over my head will help my concentration....
--b.
next prev parent reply other threads:[~2012-04-17 17:06 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-17 5:25 [git pull] vfs and fs fixes Al Viro
2012-04-17 15:01 ` Linus Torvalds
2012-04-17 16:22 ` J. Bruce Fields
2012-04-17 16:33 ` Linus Torvalds
2012-04-17 16:33 ` Linus Torvalds
2012-04-17 17:06 ` J. Bruce Fields [this message]
2012-04-17 17:06 ` J. Bruce Fields
2012-04-17 17:59 ` Al Viro
2012-04-17 18:01 ` Al Viro
2012-04-17 18:28 ` Al Viro
2012-04-17 21:14 ` J. Bruce Fields
2012-04-17 22:08 ` Linus Torvalds
2012-04-17 23:44 ` Al Viro
2012-04-18 0:49 ` J. Bruce Fields
2012-04-18 0:56 ` Linus Torvalds
2012-04-18 21:52 ` J. Bruce Fields
2012-04-25 15:20 ` J. Bruce Fields
2012-04-25 15:22 ` [PATCH 1/5] vfs: fix outdated i_mutex_lock_class documentation bfields
2012-04-25 15:22 ` [PATCH 2/5] vfs: pull ext4's double-i_mutex-locking into common code bfields
2012-04-25 15:22 ` [PATCH 3/5] vfs: don't use PARENT/CHILD lock classes for non-directories bfields
2012-04-25 15:22 ` [PATCH 4/5] vfs: take i_mutex on renamed file bfields
2012-04-25 15:22 ` [PATCH 5/5] vfs: change nondirectory i_mutex ordering to fix quota deadlock bfields
2012-04-25 15:28 ` J. Bruce Fields
2012-04-25 19:53 ` Jan Kara
2012-04-25 19:58 ` J. Bruce Fields
2012-04-20 11:15 ` [git pull] vfs and fs fixes Jan Kara
2012-04-24 19:52 ` J. Bruce Fields
2012-04-24 22:23 ` Jan Kara
2012-04-25 11:29 ` J. Bruce Fields
2012-04-25 16:26 ` Jan Kara
2012-04-25 16:47 ` Steven Whitehouse
2012-04-25 17:11 ` J. Bruce Fields
2012-04-18 0:47 ` J. Bruce Fields
2012-04-19 3:23 ` Benjamin Herrenschmidt
2012-04-19 14:50 ` Ted Ts'o
2012-04-24 17:40 ` Greg KH
2012-04-24 17:45 ` Al Viro
2012-04-24 17:59 ` Greg KH
2012-04-24 18:04 ` Al Viro
2012-04-24 20:37 ` Greg KH
-- strict thread matches above, loose matches on Subject: below --
2013-09-18 22:52 Al Viro
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