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Date: Tue, 6 Sep 2016 13:49:37 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Felipe Balbi <felipe.balbi@linux.intel.com>
Cc: Alan Stern <stern@rowland.harvard.edu>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
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        Will Deacon <will.deacon@arm.com>
Subject: Re: Memory barrier needed with wake_up_process()?
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On Tue, Sep 06, 2016 at 02:43:39PM +0300, Felipe Balbi wrote:

> > Could you confirm that bulk_{in,out}_complete() work on different
> > usb_request structures, and they can not, at any time, get called on the
> > _same_ request?
> 
> usb_requests are allocated for a specific endpoint and USB Device
> Controller (UDC) drivers refuse to queue requests allocated for epX to
> epY, so this really can never happen.

Good, thanks!

> My fear now, however, is that changing smp_[rw]mb() to smp_mb() just
> adds extra overhead which makes the problem much, much less likely to
> happen. Does that sound plausible to you?

I did consider that, but I've not sufficiently grokked the code to rule
out actual fail. So let me stare at this a bit more.