linux-kernel - Re: loop: fix deadlock when sysfs and LOOP_CLR

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Message-ID: <CAPXgP11W7dKSAQaemaeN=7desPtK-VonTLvLoW9_i1rUbYjvJg@mail.gmail.com>
Date:	Sun, 31 Jul 2011 22:42:59 +0200
From:	Kay Sievers <kay.sievers@...y.org>
To:	Jens Axboe <jaxboe@...ionio.com>
Cc:	Milan Broz <mbroz@...hat.com>, Tejun Heo <tj@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: loop: fix deadlock when sysfs and LOOP_CLR_FD race against each other

On Sun, Jul 31, 2011 at 22:20, Jens Axboe <jaxboe@...ionio.com> wrote:
> On 2011-07-30 21:19, Kay Sievers wrote:
>> Instead of taking the lo_ctl_mutex from sysfs code, take the inner
>> lo->lo_lock, to protect the access to the backing_file data.
>>
>> Thanks to Tejun for help debugging and finding a solution.
>
> Looks good, looks like something that should have a stable tag as well?

Right, I think it makes sense to have that in -stable.

It's pretty hard to trigger, I had multiple threads running, crawling
/sys and adding/binding/unbinding/removing 1000s of loop devices, and
it takes several minutes sometimes until its hit. So I only tested it
on top of the 3 loop-control patches, but the issue should exist in
the current code as well.

Thanks,
Kay
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