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Date:   Mon, 10 Jan 2022 17:40:54 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Jan Kara <jack@suse.cz>
Cc:     Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
        Dan Schatzberg <schatzberg.dan@gmail.com>,
        kernel test robot <oliver.sang@intel.com>,
        Jan Stancek <jstancek@redhat.com>,
        linux-block <linux-block@vger.kernel.org>
Subject: Re: [PATCH v2 2/2] loop: use task_work for autoclear operation
Message-ID: <20220110164054.GA7047@lst.de>
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On Mon, Jan 10, 2022 at 02:42:34PM +0100, Jan Kara wrote:
> I see. But:
> a) We didn't fully establish a real deadlock scenario from the lockdep
> report, did we? The lockdep report involved suspend locks, some locks on
> accessing files in /proc etc. and it was not clear whether it all reflects
> a real deadlock possibility or just a fact that lockdep tracking is rather
> coarse-grained at times. Now lockdep report is unpleasant and loop device
> locking was ugly anyway so your async change made sense but once lockdep is
> silenced we should really establish whether there is real deadlock and more
> work is needed or not.
> 
> b) Unless we have a realistic plan of moving *all* blk_mq_freeze_queue()
> calls from under open_mutex in loop driver, moving stuff "where possible"
> from under open_mutex is IMO just muddying water.

Agreed.  I also have to say I'm not a fan of proliferating the use of
task_work_add.