From: Will Deacon <will.deacon@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>,
linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
manfred@colorfullife.com, dave@stgolabs.net,
paulmck@linux.vnet.ibm.com, Waiman.Long@hpe.com, tj@kernel.org,
pablo@netfilter.org, kaber@trash.net, davem@davemloft.net,
oleg@redhat.com, netfilter-devel@vger.kernel.org,
sasha.levin@oracle.com, hofrat@osadl.org, jejb@parisc-linux.org,
chris@zankel.net, rth@twiddle.net, dhowells@redhat.com,
schwidefsky@de.ibm.com, mpe@ellerman.id.au, ralf@linux-mips.org,
linux@armlinux.org.uk, rkuo@codeaurora.org, vgupta@synopsys.com,
james.hogan@imgtec.com, realmz6@gmail.com,
ysato@users.sourceforge.jp, tony.luck@intel.com,
cmetcalf@mellanox.com, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH -v4 5/7] locking, arch: Update spin_unlock_wait()
Date: Fri, 3 Jun 2016 18:35:37 +0100 [thread overview]
Message-ID: <20160603173537.GR9915@arm.com> (raw)
In-Reply-To: <20160603134249.GA3693@twins.programming.kicks-ass.net>
On Fri, Jun 03, 2016 at 03:42:49PM +0200, Peter Zijlstra wrote:
> On Fri, Jun 03, 2016 at 01:47:34PM +0100, Will Deacon wrote:
> > Even on x86, I think you need a fence here:
> >
> > X86 lock
> > {
> > }
> > P0 | P1 ;
> > MOV EAX,$1 | MOV EAX,$1 ;
> > LOCK XCHG [x],EAX | LOCK XCHG [y],EAX ;
> > MOV EBX,[y] | MOV EBX,[x] ;
> > exists
> > (0:EAX=0 /\ 0:EBX=0 /\ 1:EAX=0 /\ 1:EBX=0)
> >
> > is permitted by herd.
>
> I am puzzled.. this should not be. You say adding MFENCE after LOCK XCHG
> makes it 'work', but we assume LOCK <op> is a full fence all over the
> place.
>
> I'm thinking herd is busted.
FWIW -- I spoke to the Herd authors and they confirmed that this is a
regresion in herd (fixed in the bleeding edge version).
Will
next prev parent reply other threads:[~2016-06-03 17:35 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-02 11:51 [PATCH -v4 0/7] spin_unlock_wait borkage and assorted bits Peter Zijlstra
2016-06-02 11:51 ` [PATCH -v4 1/7] locking: Replace smp_cond_acquire with smp_cond_load_acquire Peter Zijlstra
2016-06-02 11:51 ` [PATCH -v4 2/7] locking: Introduce smp_acquire__after_ctrl_dep Peter Zijlstra
2016-06-02 11:52 ` [PATCH -v4 3/7] locking: Move smp_cond_load_acquire() to asm-generic/barrier.h Peter Zijlstra
2016-06-02 11:52 ` [PATCH -v4 4/7] locking, tile: Provide TILE specific smp_acquire__after_ctrl_dep Peter Zijlstra
2016-06-02 11:52 ` [PATCH -v4 5/7] locking, arch: Update spin_unlock_wait() Peter Zijlstra
2016-06-02 14:24 ` Boqun Feng
2016-06-02 14:44 ` Peter Zijlstra
2016-06-02 15:11 ` Boqun Feng
2016-06-02 15:57 ` Boqun Feng
2016-06-02 16:04 ` Peter Zijlstra
2016-06-02 16:34 ` Peter Zijlstra
2016-06-02 17:57 ` Will Deacon
2016-06-02 21:51 ` Peter Zijlstra
2016-06-03 12:47 ` Will Deacon
2016-06-03 13:42 ` Peter Zijlstra
2016-06-03 17:35 ` Will Deacon [this message]
2016-06-03 19:13 ` Peter Zijlstra
2016-06-03 13:48 ` Peter Zijlstra
2016-06-06 16:08 ` Peter Zijlstra
2016-06-07 11:43 ` Boqun Feng
2016-06-07 12:00 ` Peter Zijlstra
2016-06-07 12:45 ` Boqun Feng
2016-06-07 17:36 ` Peter Zijlstra
2016-06-02 11:52 ` [PATCH -v4 6/7] locking: Update spin_unlock_wait users Peter Zijlstra
2016-06-02 11:52 ` [PATCH -v4 7/7] locking,netfilter: Fix nf_conntrack_lock() Peter Zijlstra
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