From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752676Ab3GIPvY (ORCPT ); Tue, 9 Jul 2013 11:51:24 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37573 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751653Ab3GIPvW (ORCPT ); Tue, 9 Jul 2013 11:51:22 -0400 From: Jiri Olsa To: linux-kernel@vger.kernel.org Cc: Jiri Olsa , Corey Ashford , Frederic Weisbecker , Ingo Molnar , Namhyung Kim , Paul Mackerras , Peter Zijlstra , Arnaldo Carvalho de Melo , Vince Weaver Subject: [PATCH 2/2] perf: Remove WARN_ON_ONCE check in __perf_event_enable for valid scenario Date: Tue, 9 Jul 2013 17:44:11 +0200 Message-Id: <1373384651-6109-2-git-send-email-jolsa@redhat.com> In-Reply-To: <1373384651-6109-1-git-send-email-jolsa@redhat.com> References: <1373384651-6109-1-git-send-email-jolsa@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The '!ctx->is_active' check has a valid scenario, so there's no need for the WARN macro. The reason is that there's a time window between 'ctx->is_active' check in perf_event_enable function and __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 WARN below. Removing the WARN_ON_ONCE check. [ 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 Cc: Corey Ashford Cc: Frederic Weisbecker Cc: Ingo Molnar Cc: Namhyung Kim Cc: Paul Mackerras Cc: Peter Zijlstra Cc: Arnaldo Carvalho de Melo Cc: Vince Weaver --- 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 446ec3d..eba8fb5 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -1963,7 +1963,16 @@ 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); -- 1.7.11.7