From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754753AbdGXWOe (ORCPT ); Mon, 24 Jul 2017 18:14:34 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:52557 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932212AbdGXWNQ (ORCPT ); Mon, 24 Jul 2017 18:13:16 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, "Paul E. McKenney" , Ingo Molnar , Will Deacon , Alan Stern , Andrea Parri , Linus Torvalds Subject: [PATCH tip/core/rcu 4/9] completion: Replace spin_unlock_wait() with lock/unlock pair Date: Mon, 24 Jul 2017 15:13:04 -0700 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20170724221252.GA14238@linux.vnet.ibm.com> References: <20170724221252.GA14238@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17072422-0040-0000-0000-000003850BF4 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007419; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000214; SDB=6.00892382; UDB=6.00446027; IPR=6.00672546; BA=6.00005489; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00016356; XFM=3.00000015; UTC=2017-07-24 22:13:12 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17072422-0041-0000-0000-000007792923 Message-Id: <1500934389-14942-4-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-07-24_14:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=1 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1706020000 definitions=main-1707240340 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org There is no agreed-upon definition of spin_unlock_wait()'s semantics, and it appears that all callers could do just as well with a lock/unlock pair. This commit therefore replaces the spin_unlock_wait() call in completion_done() with spin_lock() followed immediately by spin_unlock(). This should be safe from a performance perspective because the lock will be held only the wakeup happens really quickly. Signed-off-by: Paul E. McKenney Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Will Deacon Cc: Alan Stern Cc: Andrea Parri Cc: Linus Torvalds --- kernel/sched/completion.c | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-) diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c index 13fc5ae9bf2f..3feb218171a9 100644 --- a/kernel/sched/completion.c +++ b/kernel/sched/completion.c @@ -307,14 +307,9 @@ bool completion_done(struct completion *x) * If ->done, we need to wait for complete() to release ->wait.lock * otherwise we can end up freeing the completion before complete() * is done referencing it. - * - * The RMB pairs with complete()'s RELEASE of ->wait.lock and orders - * the loads of ->done and ->wait.lock such that we cannot observe - * the lock before complete() acquires it while observing the ->done - * after it's acquired the lock. */ - smp_rmb(); - spin_unlock_wait(&x->wait.lock); + spin_lock_irq(&x->wait.lock); + spin_unlock_irq(&x->wait.lock); return true; } EXPORT_SYMBOL(completion_done); -- 2.5.2