From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752668AbeDHV70 (ORCPT ); Sun, 8 Apr 2018 17:59:26 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:43228 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752188AbeDHV7Y (ORCPT ); Sun, 8 Apr 2018 17:59:24 -0400 Date: Sun, 8 Apr 2018 15:00:21 -0700 From: "Paul E. McKenney" To: Randy Dunlap Cc: Andrea Parri , linux-kernel@vger.kernel.org, Alan Stern , David Howells , Will Deacon , Peter Zijlstra , Boqun Feng , Nicholas Piggin , Jade Alglave , Luc Maranget , Akira Yokosawa , Ingo Molnar Subject: Re: [PATCH v4 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> <1523044060-5568-1-git-send-email-andrea.parri@amarulasolutions.com> <20180406210741.GF3948@linux.vnet.ibm.com> <30d15756-1cb4-7123-b4d9-ce2e66861df3@infradead.org> <20180406215825.GA3646@andrea> <20180408211446.GU3948@linux.vnet.ibm.com> <2a404a5a-de6b-8cf8-325a-9c6c2d78bc10@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2a404a5a-de6b-8cf8-325a-9c6c2d78bc10@infradead.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18040821-0040-0000-0000-00000413616D X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008820; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000256; SDB=6.01015083; UDB=6.00517545; IPR=6.00794334; MB=3.00020476; MTD=3.00000008; XFM=3.00000015; UTC=2018-04-08 21:59:23 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18040821-0041-0000-0000-000008147A03 Message-Id: <20180408220021.GY3948@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-04-08_06:,, 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-1804080241 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Apr 08, 2018 at 02:32:53PM -0700, Randy Dunlap wrote: > On 04/08/2018 02:14 PM, Paul E. McKenney wrote: > > On Fri, Apr 06, 2018 at 11:58:25PM +0200, Andrea Parri wrote: > >> On Fri, Apr 06, 2018 at 02:08:16PM -0700, Randy Dunlap wrote: > >>> On 04/06/2018 02:07 PM, Paul E. McKenney wrote: > >>>> On Fri, Apr 06, 2018 at 02:01:41PM -0700, Randy Dunlap wrote: > >>>>> On 04/06/2018 12:47 PM, 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(). Also, > >>>>>> describe behaviors specific to certain CONFIG_SMP=n builds. > >>>>>> > >>>>>> [1] https://marc.info/?l=linux-kernel&m=151981440005264&w=2 > >>>>>> https://marc.info/?l=linux-kernel&m=152042843808540&w=2 > >>>>>> https://marc.info/?l=linux-kernel&m=152043346110262&w=2 > >>>>>> > >>>>>> Co-Developed-by: Andrea Parri > >>>>>> Co-Developed-by: Alan Stern > >>>>>> Co-Developed-by: David Howells > >>>>>> Signed-off-by: Andrea Parri > >>>>>> Signed-off-by: Alan Stern > >>>>>> Signed-off-by: David Howells > >>>>>> Cc: Will Deacon > >>>>>> Cc: Peter Zijlstra > >>>>>> Cc: Boqun Feng > >>>>>> Cc: Nicholas Piggin > >>>>>> Cc: Jade Alglave > >>>>>> Cc: Luc Maranget > >>>>>> Cc: "Paul E. McKenney" > >>>>>> Cc: Akira Yokosawa > >>>>>> Cc: Ingo Molnar > >>>>>> --- > >>>>>> include/linux/spinlock.h | 18 ++++++++++++++++++ > >>>>>> 1 file changed, 18 insertions(+) > >>>>>> > >>>>>> diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h > >>>>>> index 4894d322d2584..1e8a464358384 100644 > >>>>>> --- a/include/linux/spinlock.h > >>>>>> +++ b/include/linux/spinlock.h > >>>>>> @@ -380,6 +380,24 @@ 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. > >>>>>> + * > >>>>>> + * Returns: 1 if @lock is locked, 0 otherwise. > >>>>> > >>>>> Sorry, minor nit: > >>>>> s/Returns:/Return:/ > >>>>> (according to kernel-doc.rst) > >>>>> > >>>>> although I agree that "Returns:" is better. > >>>>> [I should have changed that years ago.] > >>>> > >>>> Agreed, English grammar and templates often seem to conflict. > >>>> > >>>> So should we change this comment, or are you instead proposing to add > >>>> "Returns:" as valid kernel-doc? > >>> > >>> Please change this patch to current doc syntax. > >>> Any changes to kernel-doc syntax would come later. > > > > Are you sure? > > > > $ git grep "\* Returns:" | wc -l > > 2470 > > $ git grep "\* Return:" | wc -l > > 4144 > > > > Looks like more than a third of them are already "Returns:". ;-) > > > >> Paul: I understand that you're going to do this change "in place"; please > >> let me know if I'm wrong/if you need a new submission. > > > > If Randy is certain that he would like to continue propagating > > this grammatical infelicity, sure. ;-) > > eh? > Well, Documentation/doc-guide/kernel-doc.rst says "Return:", but it appears > that it does not matter to scripts/kernel-doc -- it's just the name of a > "section" of the documentation and can be spelled any way! oh well. :) > > Acked-by: Randy Dunlap Applied, thank you both! Thanx, Paul