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: <49AA599B.8040308@gmail.com>
Date:	Sun, 01 Mar 2009 10:47:07 +0100
From:	Jiri Slaby <jirislaby@...il.com>
To:	Dave Young <hidave.darkstar@...il.com>
CC:	Al Viro <viro@...iv.linux.org.uk>, 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 28.4.2008 04:33, Dave Young wrote:
> On Mon, Apr 28, 2008 at 10:15 AM, Al Viro<viro@...iv.linux.org.uk>  wrote:
>> On Mon, Apr 28, 2008 at 03:13:09AM +0100, Al Viro wrote:
>>   >  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.
>
> Hi, Maybe I have some mis-understood, thanks for pointing out in advance.
>
> IMO the lo_ctl_mutex is for the lo->* state locking,  they are all set
> to proper values before fput(filp), so I think it's safe to do that.
>
>>   BTW, explain also why open() at that spot will not do interesting things
>>   wrt BLKRRPART done a bit below, please.
>>
>
> open with a loop device unbound? Sorry, I don't understand.  Could you
> explain a bit? Thanks

Any ideas here? Al? The bug survived almost a year...

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