From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752838AbdGEXcE (ORCPT ); Wed, 5 Jul 2017 19:32:04 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:48303 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752632AbdGEXbu (ORCPT ); Wed, 5 Jul 2017 19:31:50 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: netfilter-devel@vger.kernel.org, netdev@vger.kernel.org, oleg@redhat.com, akpm@linux-foundation.org, mingo@redhat.com, dave@stgolabs.net, manfred@colorfullife.com, tj@kernel.org, arnd@arndb.de, linux-arch@vger.kernel.org, will.deacon@arm.com, peterz@infradead.org, stern@rowland.harvard.edu, parri.andrea@gmail.com, torvalds@linux-foundation.org, "Paul E. McKenney" Subject: [PATCH v2 3/9] sched: Replace spin_unlock_wait() with lock/unlock pair Date: Wed, 5 Jul 2017 16:31:37 -0700 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20170705232955.GA15992@linux.vnet.ibm.com> References: <20170705232955.GA15992@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17070523-0048-0000-0000-000001BBBC83 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007326; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000214; SDB=6.00883401; UDB=6.00440697; IPR=6.00663592; BA=6.00005454; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00016100; XFM=3.00000015; UTC=2017-07-05 23:31:47 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17070523-0049-0000-0000-000041C76D00 Message-Id: <1499297503-23852-3-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-07-05_16:,, 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=8.0.1-1703280000 definitions=main-1707050383 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 do_task_dead() with spin_lock() followed immediately by spin_unlock(). This should be safe from a performance perspective because the lock is this tasks ->pi_lock, and this is called only after the task exits. Signed-off-by: Paul E. McKenney Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Will Deacon Cc: Alan Stern Cc: Andrea Parri Cc: Linus Torvalds [ paulmck: Replace leading smp_mb() with smp_mb__before_spinlock(), courtesy of Arnd Bergmann's noting its odd location. ] --- kernel/sched/core.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index e91138fcde86..48a8760fedf4 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3460,8 +3460,9 @@ void __noreturn do_task_dead(void) * To avoid it, we have to wait for releasing tsk->pi_lock which * is held by try_to_wake_up() */ - smp_mb(); - raw_spin_unlock_wait(¤t->pi_lock); + smp_mb__before_spinlock(); + raw_spin_lock_irq(¤t->pi_lock); + raw_spin_unlock_irq(¤t->pi_lock); /* Causes final put_task_struct in finish_task_switch(): */ __set_current_state(TASK_DEAD); -- 2.5.2