linux-kernel - Re: VFS deadlock ?

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Message-ID: <20130321192146.GX21522@ZenIV.linux.org.uk>
Date:	Thu, 21 Mar 2013 19:21:46 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: VFS deadlock ?

On Thu, Mar 21, 2013 at 03:06:53PM -0400, Dave Jones wrote:
> Al, Linus,

> trinity-child2  D ffff880110b3a7e0  5448  7669      1 0x00000004
[sits in rename(), trying to grab ->i_mutex on a parent]

> 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

Wait a minute...  How the hell does it manage to sit with *two* blocked locks?
Confused...
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