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Subject: Re: sem_lock() vs qspinlocks
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>, Davidlohr Bueso <dave@stgolabs.net>,
        Manfred Spraul <manfred@colorfullife.com>,
        Waiman Long <Waiman.Long@hpe.com>, Ingo Molnar <mingo@kernel.org>,
        ggherdovich@suse.com, Mel Gorman <mgorman@techsingularity.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Will Deacon <will.deacon@arm.com>
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On Mon, May 23, 2016 at 5:25 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> Paul has smp_mb__after_unlock_lock() for the RCpc 'upgrade'. How about
> something like:
>
>         smp_mb__after_lock()

I'd much rather make the naming be higher level. It's not necessarily
going to be a "mb", and while the problem is about smp, the primitives
it is synchronizing aren't actually smp-specific (ie you're
synchronizing a lock that is relevant on UP too).

So I'd just call it something like

        spin_lock_sync_after_lock();

because different locks might have different levels of serialization
(ie maybe a spinlock needs one thing, and a mutex needs another - if
we start worrying about ordering between spin_lock and
mutex_is_locked(), for example, or between mutex_lock() and
spin_is_locked()).

Hmm?

                     Linus