From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757098AbeDBTew (ORCPT ); Mon, 2 Apr 2018 15:34:52 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:55640 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757069AbeDBTeu (ORCPT ); Mon, 2 Apr 2018 15:34:50 -0400 Date: Mon, 2 Apr 2018 12:35:40 -0700 From: "Paul E. McKenney" To: Alan Stern Cc: Andrea Parri , Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, Andrea Parri , Will Deacon , Boqun Feng , Nicholas Piggin , David Howells , Jade Alglave , Luc Maranget , Akira Yokosawa Subject: Re: [PATCH v2 1/3] locking: Document the semantics of spin_is_locked() Reply-To: paulmck@linux.vnet.ibm.com References: <1522600912-6208-2-git-send-email-andrea.parri@amarulasolutions.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18040219-2213-0000-0000-00000288E8D0 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008790; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000255; SDB=6.01012160; UDB=6.00515827; IPR=6.00791430; MB=3.00020378; MTD=3.00000008; XFM=3.00000015; UTC=2018-04-02 19:34:47 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18040219-2214-0000-0000-0000599D2444 Message-Id: <20180402193540.GB3948@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-04-02_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=3 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1804020212 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 02, 2018 at 10:03:22AM -0400, Alan Stern wrote: > On Sun, 1 Apr 2018, Andrea Parri wrote: > > > 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 | 11 +++++++++++ > > 1 file changed, 11 insertions(+) > > > > diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h > > index 4894d322d2584..2639fdc9a916c 100644 > > --- a/include/linux/spinlock.h > > +++ b/include/linux/spinlock.h > > @@ -380,6 +380,17 @@ 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. > > This is a good addition. But please remove the parenthetical phrase. > Or if you prefer to keep it, at least remove the parentheses. Unless someone objects or proposes a different course of action, I will make this change in -rcu. Thanx, Paul > Alan > > > + */ > > static __always_inline int spin_is_locked(spinlock_t *lock) > > { > > return raw_spin_is_locked(&lock->rlock); > > >