linux-kernel - Re: btrfs: lock inversion between delayed_node->mutex and found->groups

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Date:	Mon, 7 Apr 2014 15:27:04 -0400
From:	Chris Mason <clm@...com>
To:	Sasha Levin <sasha.levin@...cle.com>, <dsterba@...e.cz>,
	Jeff Mahoney <jeffm@...e.com>, <jbacik@...com>,
	<linux-btrfs@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: btrfs: lock inversion between delayed_node->mutex and found->groups_sem

On 04/07/2014 02:03 PM, Sasha Levin wrote:
> On 04/07/2014 01:17 PM, Chris Mason wrote:
>>
>>
>> On 04/07/2014 12:54 PM, David Sterba wrote:
>>> On Fri, Apr 04, 2014 at 05:15:23PM -0400, Sasha Levin wrote:
>>>> On 03/26/2014 01:01 PM, Jeff Mahoney wrote:
>>>>> On 3/17/14, 9:05 AM, David Sterba wrote:
>>>>>>> On Fri, Mar 14, 2014 at 08:12:16PM -0400, Sasha Levin wrote:
>>>>>>>>> While fuzzing with trinity inside a KVM tools guest running the latest -next kernel I've stumbled on the following:
>>>>>>>>>
>>>>>>>>> [  788.458756]        CPU0                    CPU1 [  788.459188] ----                    ---- [  788.459625] lock(&found->groups_sem); [  788.460041] local_irq_disable(); [  788.460041] lock(&delayed_node->mutex); [  788.460041] lock(&found->groups_sem); [  788.460041]   <Interrupt> [ 788.460041]     lock(&delayed_node->mutex); [  788.460041] [ 788.460041]  *** DEADLOCK *** [  788.460041] [  788.460041] 2 locks held by kswapd3/4199:
>>>>>>>
>>>>>>> I've once (3.14-rc5) seen the same warning also caused by xfstests/generic/224
>>>>> I think this is from my sysfs patches. We call kobject_add while holding the group_sem. kobject_add ultimately allocates with GFP_KERNEL, so it can enter reclaim. This particular case isn't dangerous, but it could hit while hot-adding a device. The fix should be pretty simple.
>>>>
>>>> Is that fix available anywhere? I'm still seeing the issue in -next.
>>>
>>> It is: https://urldefense.proofpoint.com/v1/url?u=https://patchwork.kernel.org/patch/3894781/&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=6%2FL0lzzDhu0Y1hL9xm%2BQyA%3D%3D%0A&m=HQJVSK4wPTft1zWwI1cGvwj5OfdmN5UItVlucU1K31o%3D%0A&s=5113699a2e7345a779333c87dd5b1d88b4410a7c7fcd5fa424baeb838ad7d31b , will probably hit -rc2
>>>
>>
>> Its in the integration branch now along with some other important fixes.  We'll get it out shortly
>
> Chris,
>
> Can I suggest adding the integration branch to linux-next as well? That way
> all the folks who report issues coming out of -next would be able to test
> the fixes as well.
>

Hi Sasha,

The ink is still a little wet on the integration branch. It'll 
definitely go to linux-next and to Linus.

-chris

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