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

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Date:   Wed, 22 Apr 2020 00:29:42 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Luis Chamberlain <mcgrof@...nel.org>
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, ming.lei@...hat.com,
        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 Mon, Apr 20, 2020 at 08:41:56PM +0000, Luis Chamberlain wrote:
> Its already there. And yes, after my changes it is technically possible
> to just re-use it directly. But this is complicated by a few things. One
> is that at this point in time, asynchronous request_queue removal is
> still possible, and so a race was exposed where a requeust_queue may be
> lingering but its old device is gone. That race is fixed by reverting us
> back to synchronous request_queue removal, therefore ensuring that the
> debugfs dir exists so long as the device does.
> 
> I can remove the debugfs_lookup() *after* we revert to synchronous
> request_queue removal, or we just re-order the patches so that the
> revert happens first. That should simplify this patch.

Yes, please move the synchronous removal first instead of working around
the current problems.