From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Josh Triplett <josh@joshtriplett.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, mingo@kernel.org,
laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
niv@us.ibm.com, tglx@linutronix.de, rostedt@goodmis.org,
dhowells@redhat.com, edumazet@google.com, darren@dvhart.com,
fweisbec@gmail.com, sbw@mit.edu,
Linux-Arch <linux-arch@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>, Oleg Nesterov <oleg@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH v5 tip/core/locking 6/7] locking: Add an smp_mb__after_unlock_lock() for UNLOCK+LOCK barrier
Date: Tue, 10 Dec 2013 12:11:54 -0800 [thread overview]
Message-ID: <20131210201154.GF4208@linux.vnet.ibm.com> (raw)
In-Reply-To: <20131210174508.GC10311@leaf>
On Tue, Dec 10, 2013 at 09:45:08AM -0800, Josh Triplett wrote:
> On Tue, Dec 10, 2013 at 01:37:26PM +0100, Peter Zijlstra wrote:
> > On Mon, Dec 09, 2013 at 05:28:02PM -0800, Paul E. McKenney wrote:
> > > diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
> > > index f89da808ce31..abf645799991 100644
> > > --- a/arch/powerpc/include/asm/barrier.h
> > > +++ b/arch/powerpc/include/asm/barrier.h
> > > @@ -84,4 +84,6 @@ do { \
> > > ___p1; \
> > > })
> > >
> > > +#define smp_mb__after_unlock_lock() do { } while (0)
> > > +
> > > #endif /* _ASM_POWERPC_BARRIER_H */
> >
> > Didn't ben said ppc actually violates the current unlock+lock assumtion
> > and therefore this barrier woulnd't actually be a nop on ppc
>
> Or, ppc could fix its lock primitives to preserve the unlock+lock
> assumption, and avoid subtle breakage across half the kernel.
Indeed. However, another motivation for this change was the difficulty
in proving that x86 really provided the equivalent of a full barrier
for the MCS lock handoff case:
http://www.spinics.net/lists/linux-mm/msg65653.html
Thanx, Paul
next prev parent reply other threads:[~2013-12-10 20:12 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20131210012738.GA24317@linux.vnet.ibm.com>
[not found] ` <1386638883-25379-1-git-send-email-paulmck@linux.vnet.ibm.com>
2013-12-10 1:27 ` [PATCH v5 tip/core/locking 3/7] Documentation/memory-barriers.txt: Prohibit speculative writes Paul E. McKenney
2013-12-10 1:28 ` [PATCH v5 tip/core/locking 6/7] locking: Add an smp_mb__after_unlock_lock() for UNLOCK+LOCK barrier Paul E. McKenney
2013-12-10 1:28 ` Paul E. McKenney
2013-12-10 1:34 ` Josh Triplett
2013-12-10 5:26 ` Paul E. McKenney
2013-12-10 18:53 ` Paul E. McKenney
2013-12-10 12:37 ` Peter Zijlstra
2013-12-10 17:17 ` Paul E. McKenney
2013-12-10 17:45 ` Josh Triplett
2013-12-10 20:11 ` Paul E. McKenney [this message]
2013-12-10 17:04 ` Oleg Nesterov
2013-12-10 17:18 ` Paul E. McKenney
2013-12-10 17:18 ` Paul E. McKenney
2013-12-10 17:32 ` Oleg Nesterov
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