From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release semantics) causing failures on arm64 (ThunderX)
Date: Fri, 11 Dec 2015 14:06:49 +0000 [thread overview]
Message-ID: <20151211140649.GI18828@arm.com> (raw)
In-Reply-To: <20151211134803.GP6356@twins.programming.kicks-ass.net>
On Fri, Dec 11, 2015 at 02:48:03PM +0100, Peter Zijlstra wrote:
> 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.
In which case, we should be able to relax the xchg in there (osq_wait_next)
too, right?
Will
next prev parent reply other threads:[~2015-12-11 14:06 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-10 19:43 Commit 81a43adae3b9 (locking/mutex: Use acquire/release semantics) causing failures on arm64 (ThunderX) David Daney
[not found] ` <SN1PR07MB21577C72379C8440A208D6BC9EEA0@SN1PR07MB2157.namprd07.prod.outlook.com>
2015-12-11 3:29 ` FW: " Andrew Pinski
2015-12-11 4:51 ` Andrew Pinski
2015-12-11 8:41 ` Peter Zijlstra
2015-12-11 12:04 ` Will Deacon
2015-12-11 12:13 ` Peter Zijlstra
2015-12-11 12:18 ` Will Deacon
2015-12-11 12:26 ` Peter Zijlstra
2015-12-11 13:33 ` Will Deacon
2015-12-11 13:48 ` Peter Zijlstra
2015-12-11 14:06 ` Will Deacon [this message]
2015-12-11 17:11 ` Peter Zijlstra
2015-12-11 17:24 ` Will Deacon
2015-12-11 22:35 ` Paul E. McKenney
2015-12-14 20:28 ` Peter Zijlstra
2015-12-15 4:36 ` Paul E. McKenney
2015-12-11 14:17 ` Davidlohr Bueso
2015-12-17 21:52 ` Jeremy Linton
2015-12-11 7:33 ` Peter Zijlstra
2015-12-11 9:59 ` Will Deacon
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