From: Nicholas Mc Guire <der.herr@hofr.at>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
linux-rt-users@vger.kernel.org,
LKML <linux-kernel@vger.kernel.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Carsten Emde <C.Emde@osadl.org>,
Thomas Gleixner <tglx@linutronix.de>,
Andreas Platschek <platschek@ict.tuwien.ac.at>
Subject: Re: allow preemption in check_task_state
Date: Mon, 10 Feb 2014 19:12:03 +0100 [thread overview]
Message-ID: <20140210181203.GA17914@opentech.at> (raw)
In-Reply-To: <20140210173833.GQ9987@twins.programming.kicks-ass.net>
On Mon, 10 Feb 2014, Peter Zijlstra wrote:
> On Mon, Feb 10, 2014 at 06:17:12PM +0100, Nicholas Mc Guire wrote:
> > maybe I'm missing/missunderstanding something here but
> > pi_unlock -> arch_spin_unlock is a full mb()
>
> Nope, arch_spin_unlock() on x86 is a single add[wb] without LOCK prefix.
>
> The lock and unlock primitives are in general specified to have ACQUIRE
> resp. RELEASE semantics.
>
> See Documentation/memory-barriers.txt for far too much head-hurting
> details.
I did check that - but from the code check it seems to me to be using a
lock prefix in the fast __add() path and an explicit smp_add() in the slow
path (arch/x86/include/asm/spinlock.h:arch_spin_unlock) the __add from
arch/x86/include/asm/cmpxchg.h does lock or am I missinterpreting this ?
the other archs I believe were all doing explicit mb()/smp_mb() in the
arch_spin_unlock - will go check this again.
thx!
hofrat
next prev parent reply other threads:[~2014-02-10 18:12 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-10 15:38 allow preemption in check_task_state Nicholas Mc Guire
2014-02-10 16:11 ` Steven Rostedt
2014-02-10 17:17 ` Nicholas Mc Guire
2014-02-10 17:38 ` Peter Zijlstra
2014-02-10 18:12 ` Nicholas Mc Guire [this message]
2014-02-10 18:16 ` Peter Zijlstra
2014-02-10 18:45 ` Nicholas Mc Guire
2014-02-10 17:52 ` Steven Rostedt
2014-02-10 18:13 ` Nicholas Mc Guire
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