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

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Date:	Mon, 7 Apr 2014 18:54:49 +0200
From:	David Sterba <dsterba@...e.cz>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Jeff Mahoney <jeffm@...e.com>, dsterba@...e.cz, clm@...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 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://patchwork.kernel.org/patch/3894781/ , will probably hit -rc2
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