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Re: Memory barrier needed with wake_up_process()?

From Will Deacon <will.deacon@arm.com>
Newsgroups linux.kernel
Subject Re: Memory barrier needed with wake_up_process()?
Date 2016-09-05 11:50 +0200
Message-ID <sdYHo-1W2-17@gated-at.bofh.it> (permalink)
References <sd2k1-3y8-13@gated-at.bofh.it> <sd36q-44B-13@gated-at.bofh.it> <sd4Yy-5fv-23@gated-at.bofh.it> <sd4Yy-5fv-21@gated-at.bofh.it>
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On Sat, Sep 03, 2016 at 12:16:29AM +0200, Peter Zijlstra wrote:
> On Sat, Sep 03, 2016 at 12:14:13AM +0200, Peter Zijlstra wrote:
> > On Fri, Sep 02, 2016 at 04:16:54PM -0400, Alan Stern wrote:
> > > 
> > > Actually, that's not entirely true (although presumably it works okay
> > > for most architectures).
> > 
> > Yeah, all load-store archs (with exception of PowerPC and ARM64 and
> > possibly MIPS) implement ACQUIRE with a general fence (after the ll/sc).
> > 
> > ( and MIPS doesn't use their fancy barriers in Linux )
> > 
> > PowerPC does the full fence for smp_mb__before_spinlock, which leaves
> > ARM64, I'm not sure its correct, but I'm way too tired to think about
> > that now.
> > 
> > The TSO archs imply full barriers with all atomic RmW ops and are
> > therefore also good.
> > 
> 
> Forgot to Cc Will. Will, does ARM64 need to make smp_mb__before_spinlock
> smp_mb() too?

Yes, probably. Just to confirm, the test is something like:


CPU0
----

Wx=1
smp_mb__before_spinlock()
LOCK(y)
Rz=0

CPU1
----

Wz=1
smp_mb()
Rx=0


and that should be forbidden?

Will

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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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