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Date:   Mon, 4 Feb 2019 09:25:27 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Ulf Hansson <ulf.hansson@linaro.org>
Cc:     Zachary Hays <zhays@lexmark.com>, Jens Axboe <axboe@kernel.dk>,
        Christoph Hellwig <hch@lst.de>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        "linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
        linux-block <linux-block@vger.kernel.org>
Subject: Re: [PATCH] mmc: block: handle complete_work on the system_highpri
 workqueue
Message-ID: <20190204082527.GA5953@lst.de>
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On Mon, Feb 04, 2019 at 07:24:43AM +0100, Ulf Hansson wrote:
> > The above results in multiple hung tasks that lead to failures to boot.
> >
> > Switching complete_work to the system_highpri queue avoids this
> > because system_highpri is not flagged with WQ_MEM_RECLAIM. This allows
> > the host to be released without getting blocked by other claims tasks.
> >
> 
> Thanks for fix and the detailed description to the problem!

I don't think this is correct, though.  If you think of the swap
(or memory reclaim of file backed pages) case on mmc, completing
a mmc request can very much be critical for completing that memory
reclaim.  Thus we absolutely do need a WQ_MEM_RECLAIM workqueue.
You probably want to create a private WQ_MEM_RECLAIM workqueue in the
mmc code for that.