linux-kernel - Re: [RFC] deadlock with flush

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Message-ID: <1561978947.10014.12.camel@suse.com>
Date:   Mon, 01 Jul 2019 13:02:27 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Tejun Heo <tj@...nel.org>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>
Subject: Re: [RFC] deadlock with flush_work() in UAS

Am Mittwoch, den 26.06.2019, 10:38 -0400 schrieb Alan Stern:
> On Wed, 26 Jun 2019, Oliver Neukum wrote:
> 
> > Am Montag, den 24.06.2019, 10:22 -0400 schrieb Alan Stern:
> > > But that pattern makes no sense; a driver would never use it.  The 
> > > driver would just do the reset itself.
> > 
> > Correct. But UAS and storage themselves still need to use
> > WQ_MEM_RECLAIM for their workqueues, don't they?
> 
> Perhaps so for uas.  usb-storage uses a work queue only for scanning 
> targets, which doesn't interfere with the block I/O pathway.

Are you sure? What about hub_tt_work? As far as I can tell, hub_quiesce
will flush it, hence it is used in error handling.

	Regards
		Oliver