Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release semantics) causing failures on arm64 (ThunderX)

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release semantics) causing failures on arm64 (ThunderX)
Date	2015-12-11 14:50 +0100
Message-ID	<qEwf8-57t-11@gated-at.bofh.it> (permalink)
References	(5 earlier) <qEuGl-43C-3@gated-at.bofh.it> <qEuQ1-486-7@gated-at.bofh.it> <qEuQ2-486-13@gated-at.bofh.it> <qEuZI-4cP-1@gated-at.bofh.it> <qEw5t-52w-45@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Fri, Dec 11, 2015 at 01:33:14PM +0000, Will Deacon wrote:
> On Fri, Dec 11, 2015 at 01:26:47PM +0100, Peter Zijlstra wrote:

> > While we're there, the acquire in osq_wait_next() seems somewhat ill
> > documented too.
> > 
> > I _think_ we need ACQUIRE semantics there because we want to strictly
> > order the lock-unqueue A,B,C steps and we get that with:
> > 
> >  A: SC
> >  B: ACQ
> >  C: Relaxed
> > 
> > Similarly for unlock we want the WRITE_ONCE to happen after
> > osq_wait_next, but in that case we can even rely on the control
> > dependency there.
> 
> Even for the lock-unqueue case, isn't B->C ordered by a control dependency
> because C consists only of stores?

Hmm, indeed. So we could go fully relaxed on it I suppose, since the
same is true for the unlock site.


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Thread

Commit 81a43adae3b9 (locking/mutex: Use acquire/release semantics)  causing failures on arm64 (ThunderX) David Daney <ddaney@caviumnetworks.com> - 2015-12-10 20:50 +0100
  Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Andrew Pinski <pinskia@gmail.com> - 2015-12-11 04:30 +0100
    Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Andrew Pinski <andrew.pinski@caviumnetworks.com> - 2015-12-11 06:00 +0100
      Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Peter Zijlstra <peterz@infradead.org> - 2015-12-11 09:50 +0100
        Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Will Deacon <will.deacon@arm.com> - 2015-12-11 13:10 +0100
          Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Peter Zijlstra <peterz@infradead.org> - 2015-12-11 13:20 +0100
            Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Will Deacon <will.deacon@arm.com> - 2015-12-11 13:20 +0100
              Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Peter Zijlstra <peterz@infradead.org> - 2015-12-11 13:30 +0100
                Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Will Deacon <will.deacon@arm.com> - 2015-12-11 14:40 +0100
                Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Peter Zijlstra <peterz@infradead.org> - 2015-12-11 14:50 +0100
                Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Will Deacon <will.deacon@arm.com> - 2015-12-11 15:10 +0100
                Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Peter Zijlstra <peterz@infradead.org> - 2015-12-11 18:20 +0100
                Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Will Deacon <will.deacon@arm.com> - 2015-12-11 18:30 +0100
                Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-12-11 23:40 +0100
                Re: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2015-12-14 20:00 +0100
                Re: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Peter Zijlstra <peterz@infradead.org> - 2015-12-14 21:40 +0100
                Re: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-12-15 07:20 +0100
                Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Peter Zijlstra <peterz@infradead.org> - 2015-12-14 21:30 +0100
                Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-12-15 05:40 +0100
          Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Davidlohr Bueso <dave@stgolabs.net> - 2015-12-11 15:20 +0100
    Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Peter Zijlstra <peterz@infradead.org> - 2015-12-11 08:40 +0100
  Re: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Will Deacon <will.deacon@arm.com> - 2015-12-11 11:00 +0100

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