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Date: Tue, 20 Oct 2015 11:48:49 +0800
From: Boqun Feng <boqun.feng@gmail.com>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: Waiman Long <Waiman.Long@hpe.com>, Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
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        linux-kernel@vger.kernel.org, Scott J Norton <scott.norton@hpe.com>,
        Douglas Hatch <doug.hatch@hpe.com>
Subject: Re: [PATCH tip/locking/core v8 1/5] locking/qspinlock: Use
 _acquire/_release versions of cmpxchg & xchg
Message-ID: <20151020034849.GA17714@fixme-laptop.cn.ibm.com>
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On Mon, Oct 19, 2015 at 08:46:02PM -0700, Davidlohr Bueso wrote:
> On Tue, 20 Oct 2015, Boqun Feng wrote:
>=20
> >>@@ -93,7 +94,7 @@ static __always_inline void queued_spin_unlock(struct=
 qspinlock *lock)
> >> 	/*
> >> 	 * smp_mb__before_atomic() in order to guarantee release semantics
> >> 	 */
> >>-	smp_mb__before_atomic_dec();
> >>+	smp_mb__before_atomic();
> >> 	atomic_sub(_Q_LOCKED_VAL, &lock->val);
> >
> >Just be curious, you don't use atomic_sub_release() here on purpose?
>=20
> atomic_sub() does not imply barriers, so there's no relaxed variants; tha=
t's
> only for _return() (and such) to the caller.
>=20

Ah.. my mistake ;-(

Thank you.

Regards,
Boqun

> Thanks,
> Davidlohr



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