From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753071AbeDCTbv (ORCPT ); Tue, 3 Apr 2018 15:31:51 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:37635 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752973AbeDCTbt (ORCPT ); Tue, 3 Apr 2018 15:31:49 -0400 X-Google-Smtp-Source: AIpwx4+S2CXTX8krX9XxxygoCPIFS8r/mPjQT2280t0uWepDRHAXgKy+eCNDMPvoNObsBlBi7I299w== Date: Tue, 3 Apr 2018 21:31:39 +0200 From: Andrea Parri To: David Howells Cc: paulmck@linux.vnet.ibm.com, Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, Andrea Parri , Alan Stern , Will Deacon , Boqun Feng , Nicholas Piggin , Jade Alglave , Luc Maranget , Akira Yokosawa Subject: Re: [PATCH v2 1/3] locking: Document the semantics of spin_is_locked() Message-ID: <20180403193139.GA6143@andrea> References: <20180403140715.GA5375@andrea> <20180403133543.GA26653@andrea> <1522600912-6208-2-git-send-email-andrea.parri@amarulasolutions.com> <1522600912-6208-1-git-send-email-andrea.parri@amarulasolutions.com> <29562.1522759749@warthog.procyon.org.uk> <13191.1522763553@warthog.procyon.org.uk> <3766.1522768987@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3766.1522768987@warthog.procyon.org.uk> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 03, 2018 at 04:23:07PM +0100, David Howells wrote: > Andrea Parri wrote: > > > Sorry, but I don't understand your objection: are you suggesting to add > > something like "Always return 0 on !SMP" to the comment? what else? > > Something like that, possibly along with a warning that this might not be what > you want. You might actually want it to return true on !SMP, it depends on > what you're using it for. I ended up with the following revision. I hesitated on whether to refer to 'include/linux/spinlock_up.h' or not, but in the end I decided to not include the reference. Please let me know what you think about this. Andrea >>From 85f2d12d4ad9769cc9f69cc5f447fdb8c5ed4d14 Mon Sep 17 00:00:00 2001 From: Andrea Parri Date: Tue, 3 Apr 2018 21:23:07 +0200 Subject: [PATCH v3 1/3] locking: Document the semantics of spin_is_locked() There appeared to be a certain, recurrent uncertainty concerning the semantics of spin_is_locked(), likely a consequence of the fact that this semantics remains undocumented or that it has been historically linked to the (likewise unclear) semantics of spin_unlock_wait(). A recent auditing [1] of the callers of the primitive confirmed that none of them are relying on particular ordering guarantees; document this semantics by adding a docbook header to spin_is_locked(). [1] https://marc.info/?l=linux-kernel&m=151981440005264&w=2 Signed-off-by: Andrea Parri Cc: Alan Stern Cc: Will Deacon Cc: Peter Zijlstra Cc: Boqun Feng Cc: Nicholas Piggin Cc: David Howells Cc: Jade Alglave Cc: Luc Maranget Cc: "Paul E. McKenney" Cc: Akira Yokosawa Cc: Ingo Molnar --- include/linux/spinlock.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h index 4894d322d2584..636a4436191c1 100644 --- a/include/linux/spinlock.h +++ b/include/linux/spinlock.h @@ -380,6 +380,20 @@ static __always_inline int spin_trylock_irq(spinlock_t *lock) raw_spin_trylock_irqsave(spinlock_check(lock), flags); \ }) +/** + * spin_is_locked() - Check whether a spinlock is locked. + * @lock: Pointer to the spinlock. + * + * This function is NOT required to provide any memory ordering + * guarantees; it could be used for debugging purposes or, when + * additional synchronization is needed, accompanied with other + * constructs (memory barriers) enforcing the synchronization. + * + * Return: 1, if @lock is (found to be) locked; 0, otherwise. + * + * Remark that this primitve can return a fixed value + * under certain !SMP configurations. + */ static __always_inline int spin_is_locked(spinlock_t *lock) { return raw_spin_is_locked(&lock->rlock); -- 2.7.4 > > David