linux-kernel - Re: [PATCH v2 03/10] blktrace: fix debugfs use after free

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Date:   Fri, 24 Apr 2020 23:47:41 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, axboe@...nel.dk,
        viro@...iv.linux.org.uk, bvanassche@....org, rostedt@...dmis.org,
        mingo@...hat.com, jack@...e.cz, nstange@...e.de,
        akpm@...ux-foundation.org, mhocko@...e.com, yukuai3@...wei.com,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Omar Sandoval <osandov@...com>,
        Hannes Reinecke <hare@...e.com>,
        Michal Hocko <mhocko@...nel.org>,
        syzbot+603294af2d01acfdd6da@...kaller.appspotmail.com
Subject: Re: [PATCH v2 03/10] blktrace: fix debugfs use after free

On Wed, Apr 22, 2020 at 05:43:20PM +0800, Ming Lei wrote:
> On Wed, Apr 22, 2020 at 07:28:59AM +0000, Luis Chamberlain wrote:
> > At this point in time patch-wise we still haven't reverted back to
> > synchronous request_queue removal. Considering this, a race with the
> > parent disappearing can happen because the request_queue removal is
> > deferred, that is, the request_queue's kobject's release() call used
> > schedule_work() to finish off its removal. We expect the last
> > blk_put_queue() to be called at the end of blk_cleanup_queue(). Since
> 
> Actually no, we expect that request queue is released after disk is
> released. Don't forget that gendisk does hold one extra refcount of
> request queue.

Then by all means using blk_put_queue() from everywhere should be safe
in atomic context, as we have control over that blk_put_queue() on the
block layer.

(Modulo, we accept the races possible today on blk_get_queue(), which
I'll try to address).

  Luis