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Date: Thu, 2 Mar 2006 02:54:06 +0000
From: Al Viro <viro@ftp.linux.org.uk>
To: Joshua Hudson <joshudson@gmail.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Possible deadlock in vfs layer, namei.c
Message-ID: <20060302025406.GV27946@ftp.linux.org.uk>
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On Wed, Mar 01, 2006 at 06:46:42PM -0800, Joshua Hudson wrote:
> I've been hunting down various deadlocks caused by hard links to directories.
> I found one that can happen *without* such things.
 
> process 1 does: rename("dir/subdir/file", "dir/file")
> process 2 does: rmdir("dir/subdir")
> 
> from namei.c (function: lock_rename), rename takes:
> 1. s_vfs_rename_sem,
> 2. dir/subdir: p1->d_inode->i_sem
> 3. dir: p2->d_inode->i_sem

No, it doesn't.  Wrong order - it will take dir before dir/subdir.
RTFM - Documentation/filesystems/directory-locking is there for
purpose.