linux-kernel - Re: [PATCH v2] blk-cgroup: remove entries in blkg

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Message-ID: <20180411145123.GJ793541@devbig577.frc2.facebook.com>
Date:   Wed, 11 Apr 2018 07:51:23 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Alexandru Moise <00moses.alexander00@...il.com>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Bart Van Assche <bart.vanassche@....com>
Cc:     axboe@...nel.dk, shli@...com, nborisov@...e.com, arnd@...db.de,
        gregkh@...uxfoundation.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] blk-cgroup: remove entries in blkg_tree before queue
 release

Hello,

(cc'ing Bart)

On Wed, Apr 11, 2018 at 07:46:16AM -0700, Tejun Heo wrote:
> Hello,
> 
> On Wed, Apr 11, 2018 at 04:28:59PM +0200, Alexandru Moise wrote:
> > > Ah, that changed recently.  Can you please check out the current
> > > upstream git master?
> > > 
> > Just did, without my patch I see this crash:
> 
> lol I was looking at the old tree, so this is the fix for the new
> breakage introduced by the recent change.  Sorry about the confusion.
> Joseph, can you please take a look?

Oh, it wasn't Joseph's change.  It was Bart's fix for a problem
reported by Joseph.  Bart, a063057d7c73 ("block: Fix a race between
request queue removal and the block cgroup controller") created a
regression where a request_queue can be destroyed with blkgs still
attached.  The original report is..

 http://lkml.kernel.org/r/20180407102148.GA9729@gmail.com

Thanks.

-- 
tejun