linux-kernel - Re: [PATCH 2/2] loop : Don't hold the lo_ctl_mutex while fput in loop_clr

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Message-ID: <20080428021309.GZ5882@ZenIV.linux.org.uk>
Date:	Mon, 28 Apr 2008 03:13:09 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Dave Young <hidave.darkstar@...il.com>
Cc:	linux-kernel@...r.kernel.org, jens.axboe@...cle.com
Subject: Re: [PATCH 2/2] loop : Don't hold the lo_ctl_mutex while fput in
	loop_clr_fd

On Mon, Apr 28, 2008 at 10:10:22AM +0800, Dave Young wrote:
> [Fixing bug 10504]
> 
> If the bakingfile is a block device file, losetuo -d will trigger lockdep
> warning of "circular locking dependency".
> 
> open/release lock order : bdev->bd_mutex ---> lo->lo_ctl_mutex
> loop_clr_fd lock order  : lo->lo_ctl_mutex ---> bdev->bd_mutex (fput)
> 
> Don't hold the lo_ctl_mutex while fput in loop_clr_fd to fix it. It's safe
> because all loop device state will be consistent here.

Explain.
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