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

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Message-ID: <20180411200245.GQ793541@devbig577.frc2.facebook.com>
Date:   Wed, 11 Apr 2018 13:02:45 -0700
From:   "tj@...nel.org" <tj@...nel.org>
To:     Bart Van Assche <Bart.VanAssche@....com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "nborisov@...e.com" <nborisov@...e.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>, "shli@...com" <shli@...com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "00moses.alexander00@...il.com" <00moses.alexander00@...il.com>,
        "joseph.qi@...ux.alibaba.com" <joseph.qi@...ux.alibaba.com>,
        "arnd@...db.de" <arnd@...db.de>
Subject: Re: [PATCH v2] blk-cgroup: remove entries in blkg_tree before queue
 release

On Wed, Apr 11, 2018 at 08:00:29PM +0000, Bart Van Assche wrote:
> On Wed, 2018-04-11 at 12:57 -0700, tj@...nel.org wrote:
> > On Wed, Apr 11, 2018 at 01:55:25PM -0600, Bart Van Assche wrote:
> > > On 04/11/18 13:00, Alexandru Moise wrote:
> > > > But the root cause of it is in blkcg_init_queue() when blkg_create() returns
> > > > an ERR ptr, because it tries to insert into a populated index into blkcg->blkg_tree,
> > > > the entry that we fail to remove at __blk_release_queue().
> > > 
> > > Hello Alex,
> > > 
> > > Had you considered something like the untested patch below?
> > 
> > But queue init shouldn't fail here, right?
> 
> Hello Tejun,
> 
> Your question is not entirely clear to me. Are you referring to the atomic
> allocations in blkg_create() or are you perhaps referring to something else?

Hmm.. maybe I'm confused but I thought that the fact that
blkcg_init_queue() fails itself is already a bug, which happens
because a previously destroyed queue left behind blkgs.

Thanks.

-- 
tejun