From: Chris Metcalf <cmetcalf@mellanox.com>
To: Peter Zijlstra <peterz@infradead.org>,
<linux-kernel@vger.kernel.org>, <torvalds@linux-foundation.org>,
<manfred@colorfullife.com>, <dave@stgolabs.net>,
<paulmck@linux.vnet.ibm.com>, <will.deacon@arm.com>
Cc: <boqun.feng@gmail.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>, <rth@twiddle.net>,
<vgupta@synopsys.com>, <linux@armlinux.org.uk>,
<realmz6@gmail.com>, <rkuo@codeaurora.org>, <tony.luck@intel.com>,
<james.hogan@imgtec.com>, <ralf@linux-mips.org>,
<dhowells@redhat.com>, <jejb@parisc-linux.org>,
<mpe@ellerman.id.au>, <schwidefsky@de.ibm.com>,
<ysato@users.sourceforge.jp>, <chris@zankel.net>
Subject: Re: [PATCH -v2 4/6] locking, arch: Update spin_unlock_wait()
Date: Thu, 26 May 2016 17:10:36 -0400 [thread overview]
Message-ID: <bff5e0b4-c572-cf4c-82fe-a672b8b5fb14@mellanox.com> (raw)
In-Reply-To: <20160526142354.293350777@infradead.org>
On 5/26/2016 10:19 AM, Peter Zijlstra wrote:
> --- a/arch/tile/lib/spinlock_32.c
> +++ b/arch/tile/lib/spinlock_32.c
> @@ -72,10 +72,14 @@ void arch_spin_unlock_wait(arch_spinlock
> if (next == curr)
> return;
>
> + smp_rmb();
> +
> /* Wait until the current locker has released the lock. */
> do {
> delay_backoff(iterations++);
> } while (READ_ONCE(lock->current_ticket) == curr);
> +
> + smp_acquire__after_ctrl_dep();
> }
> EXPORT_SYMBOL(arch_spin_unlock_wait);
>
> --- a/arch/tile/lib/spinlock_64.c
> +++ b/arch/tile/lib/spinlock_64.c
> @@ -72,10 +72,14 @@ void arch_spin_unlock_wait(arch_spinlock
> if (arch_spin_next(val) == curr)
> return;
>
> + smp_rmb();
> +
> /* Wait until the current locker has released the lock. */
> do {
> delay_backoff(iterations++);
> } while (arch_spin_current(READ_ONCE(lock->lock)) == curr);
> +
> + smp_acquire__after_ctrl_dep();
> }
> EXPORT_SYMBOL(arch_spin_unlock_wait);
The smp_rmb() are unnecessary for tile. We READ_ONCE next/curr from the
lock and compare them, so we know the load(s) are complete. There's no
microarchitectural speculation going on so that's that. Then we READ_ONCE
the next load on the lock from within the wait loop, so our load/load
ordering is guaranteed.
With that change,
Acked-by: Chris Metcalf <cmetcalf@mellanox.com> [for tile]
--
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com
next prev parent reply other threads:[~2016-05-26 21:11 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-26 14:19 [PATCH -v2 0/6] spin_unlock_wait borkage Peter Zijlstra
2016-05-26 14:19 ` [PATCH -v2 1/6] locking: Replace smp_cond_acquire with smp_cond_load_acquire Peter Zijlstra
2016-05-26 14:19 ` [PATCH -v2 2/6] locking: Introduce cmpwait() Peter Zijlstra
2016-05-26 14:19 ` [PATCH -v2 3/6] locking: Introduce smp_acquire__after_ctrl_dep Peter Zijlstra
2016-05-26 14:19 ` [PATCH -v2 4/6] locking, arch: Update spin_unlock_wait() Peter Zijlstra
2016-05-26 21:10 ` Chris Metcalf [this message]
2016-05-27 9:05 ` Peter Zijlstra
2016-05-27 19:34 ` Chris Metcalf
2016-05-30 9:25 ` Peter Zijlstra
2016-05-27 6:46 ` Martin Schwidefsky
2016-05-27 9:02 ` Peter Zijlstra
2016-05-26 14:19 ` [PATCH -v2 5/6] locking: Update spin_unlock_wait users Peter Zijlstra
2016-05-26 14:19 ` [PATCH -v2 6/6] locking,netfilter: Fix nf_conntrack_lock() Peter Zijlstra
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