From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754595Ab3IKEaV (ORCPT ); Wed, 11 Sep 2013 00:30:21 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:7273 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752810Ab3IKE3D (ORCPT ); Wed, 11 Sep 2013 00:29:03 -0400 X-Authority-Analysis: v=2.0 cv=R/aB6KtX c=1 sm=0 a=Sro2XwOs0tJUSHxCKfOySw==:17 a=Drc5e87SC40A:10 a=Ciwy3NGCPMMA:10 a=uJnpUzm3NeEA:10 a=5SG0PmZfjMsA:10 a=bbbx4UPp9XUA:10 a=meVymXHHAAAA:8 a=KGjhK52YXX0A:10 a=sNWqqhjsC0oA:10 a=20KFwNOVAAAA:8 a=VnNF1IyMAAAA:8 a=pGLkceISAAAA:8 a=VwQbUJbxAAAA:8 a=hGzw-44bAAAA:8 a=JfrnYn6hAAAA:8 a=M03A6vRxAPDt-7kun5cA:9 a=92Q717GQZsEA:10 a=jEp0ucaQiEUA:10 a=MSl-tDqOz04A:10 a=LI9Vle30uBYA:10 a=dowx1zmaLagA:10 a=3Rfx1nUSh_UA:10 a=jeBq3FmKZ4MA:10 a=Sro2XwOs0tJUSHxCKfOySw==:117 X-Cloudmark-Score: 0 X-Authenticated-User: X-Originating-IP: 67.255.60.225 Message-Id: <20130911042857.930603374@goodmis.org> User-Agent: quilt/0.60-1 Date: Wed, 11 Sep 2013 00:27:41 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Vince Weaver , Jiri Olsa , Peter Zijlstra , Corey Ashford , Frederic Weisbecker , Ingo Molnar , Namhyung Kim , Paul Mackerras , Arnaldo Carvalho de Melo , , Peter Zijlstra , Ingo Molnar Subject: [034/251] perf: Remove WARN_ON_ONCE() check in __perf_event_enable() for valid scenario References: <20130911042707.738353451@goodmis.org> Content-Disposition: inline; filename=0034-perf-Remove-WARN_ON_ONCE-check-in-__perf_event_enabl.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.6.11.9-rc1 stable review patch. If anyone has any objections, please let me know. ------------------ From: Jiri Olsa [ Upstream commit 06f417968beac6e6b614e17b37d347aa6a6b1d30 ] The '!ctx->is_active' check has a valid scenario, so there's no need for the warning. The reason is that there's a time window between the 'ctx->is_active' check in the perf_event_enable() function and the __perf_event_enable() function having: - IRQs on - ctx->lock unlocked where the task could be killed and 'ctx' deactivated by perf_event_exit_task(), ending up with the warning below. So remove the WARN_ON_ONCE() check and add comments to explain it all. This addresses the following warning reported by Vince Weaver: [ 324.983534] ------------[ cut here ]------------ [ 324.984420] WARNING: at kernel/events/core.c:1953 __perf_event_enable+0x187/0x190() [ 324.984420] Modules linked in: [ 324.984420] CPU: 19 PID: 2715 Comm: nmi_bug_snb Not tainted 3.10.0+ #246 [ 324.984420] Hardware name: Supermicro X8DTN/X8DTN, BIOS 4.6.3 01/08/2010 [ 324.984420] 0000000000000009 ffff88043fce3ec8 ffffffff8160ea0b ffff88043fce3f00 [ 324.984420] ffffffff81080ff0 ffff8802314fdc00 ffff880231a8f800 ffff88043fcf7860 [ 324.984420] 0000000000000286 ffff880231a8f800 ffff88043fce3f10 ffffffff8108103a [ 324.984420] Call Trace: [ 324.984420] [] dump_stack+0x19/0x1b [ 324.984420] [] warn_slowpath_common+0x70/0xa0 [ 324.984420] [] warn_slowpath_null+0x1a/0x20 [ 324.984420] [] __perf_event_enable+0x187/0x190 [ 324.984420] [] remote_function+0x40/0x50 [ 324.984420] [] generic_smp_call_function_single_interrupt+0xbe/0x130 [ 324.984420] [] smp_call_function_single_interrupt+0x27/0x40 [ 324.984420] [] call_function_single_interrupt+0x6f/0x80 [ 324.984420] [] ? _raw_spin_unlock_irqrestore+0x41/0x70 [ 324.984420] [] perf_event_exit_task+0x14d/0x210 [ 324.984420] [] ? switch_task_namespaces+0x24/0x60 [ 324.984420] [] do_exit+0x2b6/0xa40 [ 324.984420] [] ? _raw_spin_unlock_irq+0x2c/0x30 [ 324.984420] [] do_group_exit+0x49/0xc0 [ 324.984420] [] get_signal_to_deliver+0x254/0x620 [ 324.984420] [] do_signal+0x57/0x5a0 [ 324.984420] [] ? __do_page_fault+0x2a4/0x4e0 [ 324.984420] [] ? retint_restore_args+0xe/0xe [ 324.984420] [] ? retint_signal+0x11/0x84 [ 324.984420] [] do_notify_resume+0x65/0x80 [ 324.984420] [] retint_signal+0x46/0x84 [ 324.984420] ---[ end trace 442ec2f04db3771a ]--- Reported-by: Vince Weaver Signed-off-by: Jiri Olsa Suggested-by: Peter Zijlstra Cc: Corey Ashford Cc: Frederic Weisbecker Cc: Ingo Molnar Cc: Namhyung Kim Cc: Paul Mackerras Cc: Arnaldo Carvalho de Melo Cc: Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/1373384651-6109-2-git-send-email-jolsa@redhat.com Signed-off-by: Ingo Molnar Signed-off-by: Steven Rostedt --- kernel/events/core.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 073e5b9..63ffeb0 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -1708,7 +1708,16 @@ static int __perf_event_enable(void *info) struct perf_cpu_context *cpuctx = __get_cpu_context(ctx); int err; - if (WARN_ON_ONCE(!ctx->is_active)) + /* + * There's a time window between 'ctx->is_active' check + * in perf_event_enable function and this place having: + * - IRQs on + * - ctx->lock unlocked + * + * where the task could be killed and 'ctx' deactivated + * by perf_event_exit_task. + */ + if (!ctx->is_active) return -EINVAL; raw_spin_lock(&ctx->lock); -- 1.7.10.4