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Date: Thu, 21 Mar 2013 19:29:35 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Dave Jones <davej@redhat.com>, Linux Kernel <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: VFS deadlock ?
Message-ID: <20130321192935.GY21522@ZenIV.linux.org.uk>
References: <20130321190653.GA15479@redhat.com>
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On Thu, Mar 21, 2013 at 03:06:53PM -0400, Dave Jones wrote:

> Showing all locks held in the system:
> 4 locks on stack by trinity-child2/7669:
>  #0: blocked:  (sb_writers#4){.+.+.+}, instance: ffff8801292d17d8, at: [<ffffffff811df134>] mnt_want_write+0x24/0x50
>  #1: held:     (&type->s_vfs_rename_key){+.+.+.}, instance: ffff8801292d1928, at: [<ffffffff811c6f5e>] lock_rename+0x3e/0x120
>  #2: held:     (&type->i_mutex_dir_key#2/1){+.+.+.}, instance: ffff880110b3a858, at: [<ffffffff811c701e>] lock_rename+0xfe/0x120
>  #3: blocked:  (&type->i_mutex_dir_key#2/2){+.+.+.}, instance: ffff880110b3a858, at: [<ffffffff811c7034>] lock_rename+0x114/0x120

#0 oddity aside, that looks very much like directory aliased by two different
dentries.  Try to add
	BUG_ON(p1->d_inode == p2->d_inode);
just before
        mutex_lock(&p1->d_inode->i_sb->s_vfs_rename_mutex);
and see if it triggers.
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