Re: [PATCH] mmc: block: handle complete_work on the system_highpri workqueue

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On Mon, 4 Feb 2019 at 09:25, Christoph Hellwig <hch@xxxxxx> wrote:
>
> 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.

Thanks for your input!

Although, I am not sure why having our own mmc workqueue, would fix
this problem. Couldn't we hit the same kind of deadlock anyways you
think?

Kind regards
Uffe



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