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Re: Memory barrier needed with wake_up_process()?

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: Memory barrier needed with wake_up_process()?
Date 2016-09-06 13:50 +0200
Message-ID <sen33-1ra-5@gated-at.bofh.it> (permalink)
References <sdXBD-1ii-9@gated-at.bofh.it> <se40q-5xl-15@gated-at.bofh.it> <semTn-1nX-15@gated-at.bofh.it> <sen33-1ra-7@gated-at.bofh.it>
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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.

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Thread

Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-02 20:20 +0200
  Re: Memory barrier needed with wake_up_process()? "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-02 20:50 +0200
    Re: Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-02 22:30 +0200
      Re: Memory barrier needed with wake_up_process()? "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-03 11:10 +0200
      Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-03 14:40 +0200
        Re: Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-03 16:30 +0200
          Re: Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-03 16:50 +0200
            Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-05 10:40 +0200
              Re: Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-05 17:30 +0200
                Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-06 13:40 +0200
                Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-06 13:50 +0200
                Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-06 14:30 +0200
                Re: Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-06 16:50 +0200
                Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-06 17:10 +0200
                Re: Memory barrier needed with wake_up_process()? Felipe Balbi <felipe.balbi@linux.intel.com> - 2016-09-07 12:20 +0200
                Re: Memory barrier needed with wake_up_process()? Felipe Balbi <felipe.balbi@linux.intel.com> - 2016-09-06 13:50 +0200
  Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-02 21:30 +0200
    Re: Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-02 22:20 +0200
      Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-03 00:20 +0200
        Re: Memory barrier needed with wake_up_process()? Will Deacon <will.deacon@arm.com> - 2016-09-05 11:50 +0200
          Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-06 13:20 +0200
      Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-03 00:20 +0200
        Re: Memory barrier needed with wake_up_process()? Felipe Balbi <felipe.balbi@linux.intel.com> - 2016-09-03 09:00 +0200
          Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-03 14:50 +0200
            Re: Memory barrier needed with wake_up_process()? Felipe Balbi <felipe.balbi@linux.intel.com> - 2016-09-03 16:00 +0200
              Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-05 10:10 +0200
            Re: Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-03 16:20 +0200
              Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-05 10:10 +0200
                Re: Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-05 16:40 +0200
      Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-03 00:20 +0200

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