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Date: Sun, 01 Mar 2009 10:47:07 +0100
From: Jiri Slaby <jirislaby@gmail.com>
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To: Dave Young <hidave.darkstar@gmail.com>
CC: Al Viro <viro@zeniv.linux.org.uk>, linux-kernel@vger.kernel.org,
       jens.axboe@oracle.com
Subject: Re: [PATCH 2/2] loop : Don't hold the lo_ctl_mutex while fput in
 loop_clr_fd
References: <20080428021022.GB2698@darkstar.te-china.tietoenator.com>  <20080428021309.GZ5882@ZenIV.linux.org.uk>  <20080428021531.GA5882@ZenIV.linux.org.uk> <a8e1da0804271933i528d7c98m526195b361119dcf@mail.gmail.com>
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On 28.4.2008 04:33, Dave Young wrote:
> On Mon, Apr 28, 2008 at 10:15 AM, Al Viro<viro@zeniv.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...