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

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Date:	Mon, 28 Apr 2008 10:33:14 +0800
From:	"Dave Young" <hidave.darkstar@...il.com>
To:	"Al Viro" <viro@...iv.linux.org.uk>
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 10:15 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

Regards
dave
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