linux-kernel - Re: [git pull] vfs and fs fixes

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Date:	Tue, 17 Apr 2012 09:33:06 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [git pull] vfs and fs fixes

On Tue, Apr 17, 2012 at 9:22 AM, J. Bruce Fields <bfields@...ldses.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).

                  Linus
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