From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755106AbbALSaW (ORCPT ); Mon, 12 Jan 2015 13:30:22 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:58093 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753757AbbALSaD (ORCPT ); Mon, 12 Jan 2015 13:30:03 -0500 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Peter Zijlstra , Steven Rostedt , Luis Henriques Subject: [PATCH 3.16.y-ckt 138/216] tracing/sched: Check preempt_count() for current when reading task->state Date: Mon, 12 Jan 2015 18:28:36 +0000 Message-Id: <1421087394-2712-26-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1421085933-32536-1-git-send-email-luis.henriques@canonical.com> References: <1421085933-32536-1-git-send-email-luis.henriques@canonical.com> X-Extended-Stable: 3.16 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.7-ckt4 -stable review patch. If anyone has any objections, please let me know. ------------------ From: "Steven Rostedt (Red Hat)" commit aee4e5f3d3abb7a2239dd02f6d8fb173413fd02f upstream. When recording the state of a task for the sched_switch tracepoint a check of task_preempt_count() is performed to see if PREEMPT_ACTIVE is set. This is because, technically, a task being preempted is really in the TASK_RUNNING state, and that is what should be recorded when tracing a sched_switch, even if the task put itself into another state (it hasn't scheduled out in that state yet). But with the change to use per_cpu preempt counts, the task_thread_info(p)->preempt_count is no longer used, and instead task_preempt_count(p) is used. The problem is that this does not use the current preempt count but a stale one from a previous sched_switch. The task_preempt_count(p) uses saved_preempt_count and not preempt_count(). But for tracing sched_switch, if p is current, we really want preempt_count(). I hit this bug when I was tracing sleep and the call from do_nanosleep() scheduled out in the "RUNNING" state. sleep-4290 [000] 537272.259992: sched_switch: sleep:4290 [120] R ==> swapper/0:0 [120] sleep-4290 [000] 537272.260015: kernel_stack: => __schedule (ffffffff8150864a) => schedule (ffffffff815089f8) => do_nanosleep (ffffffff8150b76c) => hrtimer_nanosleep (ffffffff8108d66b) => SyS_nanosleep (ffffffff8108d750) => return_to_handler (ffffffff8150e8e5) => tracesys_phase2 (ffffffff8150c844) After a bit of hair pulling, I found that the state was really TASK_INTERRUPTIBLE, but the saved_preempt_count had an old PREEMPT_ACTIVE set and caused the sched_switch tracepoint to show it as RUNNING. Link: http://lkml.kernel.org/r/20141210174428.3cb7542a@gandalf.local.home Acked-by: Ingo Molnar Cc: Peter Zijlstra Fixes: 01028747559a "sched: Create more preempt_count accessors" Signed-off-by: Steven Rostedt Signed-off-by: Luis Henriques --- include/trace/events/sched.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h index 0a68d5ae584e..a7d67bc14906 100644 --- a/include/trace/events/sched.h +++ b/include/trace/events/sched.h @@ -100,7 +100,7 @@ static inline long __trace_sched_switch_state(struct task_struct *p) /* * For all intents and purposes a preempted task is a running task. */ - if (task_preempt_count(p) & PREEMPT_ACTIVE) + if (preempt_count() & PREEMPT_ACTIVE) state = TASK_RUNNING | TASK_STATE_MAX; #endif -- 2.1.4