Date:   Wed, 8 Dec 2021 15:12:03 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Valentin Schneider <valentin.schneider@arm.com>
Cc:     linux-kernel@vger.kernel.org,
        Abhijeet Dharmapurikar <adharmap@quicinc.com>,
        Uwe =?UTF-8?B?S2xlaW5lLUvDtm5pZw==?= 
        <u.kleine-koenig@pengutronix.de>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Juri Lelli <juri.lelli@redhat.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Kees Cook <keescook@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC PATCH 1/2] sched/tracing: Don't re-read p->state when
 emitting sched_switch event
Message-ID: <20211208151203.2196088c@gandalf.local.home>
In-Reply-To: <20211129123601.2101873-2-valentin.schneider@arm.com>
References: <20211129123601.2101873-1-valentin.schneider@arm.com>
        <20211129123601.2101873-2-valentin.schneider@arm.com>
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On Mon, 29 Nov 2021 12:36:00 +0000
Valentin Schneider <valentin.schneider@arm.com> wrote:

> As of commit
> 
>   c6e7bd7afaeb ("sched/core: Optimize ttwu() spinning on p->on_cpu")
> 
> the following sequence becomes possible:
> 
> 		      p->__state = TASK_INTERRUPTIBLE;
> 		      __schedule()
> 			deactivate_task(p);
>   ttwu()
>     READ !p->on_rq
>     p->__state=TASK_WAKING
> 			trace_sched_switch()
> 			  __trace_sched_switch_state()
> 			    task_state_index()
> 			      return 0;
> 
> TASK_WAKING isn't in TASK_REPORT, so the task appears as TASK_RUNNING in
> the trace event.
> 
> Prevent this by pushing the value read from __schedule() down the trace
> event.
> 
> Reported-by: Abhijeet Dharmapurikar <adharmap@quicinc.com>
> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> ---
>  include/linux/sched.h             | 11 ++++++++---
>  include/trace/events/sched.h      | 11 +++++++----
>  kernel/sched/core.c               |  4 ++--
>  kernel/trace/fgraph.c             |  4 +++-
>  kernel/trace/ftrace.c             |  4 +++-
>  kernel/trace/trace_events.c       |  8 ++++++--
>  kernel/trace/trace_sched_switch.c |  1 +

I believe you may have missed some functions that register the sched_switch
event. Do a git grep on register_trace_sched_switch.

-- Steve


>  7 files changed, 30 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index d2e261adb8ea..d00837d12b9d 100644