From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751985AbdGaW6Y (ORCPT ); Mon, 31 Jul 2017 18:58:24 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:54837 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751950AbdGaW6V (ORCPT ); Mon, 31 Jul 2017 18:58:21 -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" Subject: [PATCH v2 tip/core/rcu 03/10] task_work: Replace spin_unlock_wait() with lock/unlock pair Date: Mon, 31 Jul 2017 15:58:10 -0700 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20170731225754.GB2674@linux.vnet.ibm.com> References: <20170731225754.GB2674@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17073122-0056-0000-0000-000003AF981E X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007461; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000214; SDB=6.00895722; UDB=6.00448017; IPR=6.00675910; BA=6.00005503; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00016472; XFM=3.00000015; UTC=2017-07-31 22:58:19 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17073122-0057-0000-0000-000007E5C0AB Message-Id: <1501541897-5225-3-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-07-31_09:,, 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-1707310380 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Oleg Nesterov 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 task_work_run() with a spin_lock_irq() and a spin_unlock_irq() aruond the cmpxchg() dequeue loop. This should be safe from a performance perspective because ->pi_lock is local to the task and because calls to the other side of the race, task_work_cancel(), should be rare. Signed-off-by: Oleg Nesterov Signed-off-by: Paul E. McKenney --- kernel/task_work.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) diff --git a/kernel/task_work.c b/kernel/task_work.c index d513051fcca2..836a72a66fba 100644 --- a/kernel/task_work.c +++ b/kernel/task_work.c @@ -96,20 +96,16 @@ void task_work_run(void) * work->func() can do task_work_add(), do not set * work_exited unless the list is empty. */ + raw_spin_lock_irq(&task->pi_lock); do { work = READ_ONCE(task->task_works); head = !work && (task->flags & PF_EXITING) ? &work_exited : NULL; } while (cmpxchg(&task->task_works, work, head) != work); + raw_spin_unlock_irq(&task->pi_lock); if (!work) break; - /* - * Synchronize with task_work_cancel(). It can't remove - * the first entry == work, cmpxchg(task_works) should - * fail, but it can play with *work and other entries. - */ - raw_spin_unlock_wait(&task->pi_lock); do { next = work->next; -- 2.5.2