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 Kleine-König" <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>,
"Eric W. Biederman" <ebiederm@xmission.com>,
"Alexey Gladkov" <legion@kernel.org>,
"Kenta.Tada@sony.com" <Kenta.Tada@sony.com>,
"Randy Dunlap" <rdunlap@infradead.org>,
"Ed Tsai" <ed.tsai@mediatek.com>
Subject: Re: [PATCH v3 0/2] sched/tracing: sched_switch prev_state reported as TASK_RUNNING when it's not
Date: Fri, 21 Jan 2022 12:15:58 -0500 [thread overview]
Message-ID: <20220121121558.618b98e7@gandalf.local.home> (raw)
In-Reply-To: <20220120162520.570782-1-valentin.schneider@arm.com>
On Thu, 20 Jan 2022 16:25:18 +0000
Valentin Schneider <valentin.schneider@arm.com> wrote:
> Hi folks,
>
> Problem
> =======
>
> Abhijeet pointed out that the following sequence of trace events can be
> observed:
>
> cat-1676 [001] d..3 103.010411: sched_waking: comm=grep pid=1677 prio=120 target_cpu=004
> grep-1677 [004] d..2 103.010440: sched_switch: prev_comm=grep prev_pid=1677 prev_prio=120 prev_state=R 0x0 ==> next_comm=swapper/4 next_pid=0 next_prio=120
> <idle>-0 [004] dNh3 103.0100459: sched_wakeup: comm=grep pid=1677 prio=120 target_cpu=004
>
> IOW, not-yet-woken task gets presented as runnable and switched out in
> favor of the idle task... Dietmar and I had a look, turns out this sequence
> can happen:
>
> 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, hence why task_state_index(p) returns 0.
> This can happen as of commit c6e7bd7afaeb ("sched/core: Optimize ttwu()
> spinning on p->on_cpu") which punted the TASK_WAKING write to the other
> side of
>
> smp_cond_load_acquire(&p->on_cpu, !VAL);
>
> in ttwu().
>
> Uwe reported on #linux-rt what I think is a similar issue with
> TASK_RTLOCK_WAIT on PREEMPT_RT; again that state isn't in TASK_REPORT so
> you get prev_state=0 despite the task blocking on a lock.
>
> Both of those are very confusing for tooling or even human observers.
This all looks fine to me:
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Peter, want to take this through your tree?
-- Steve
next prev parent reply other threads:[~2022-01-21 17:16 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-20 16:25 [PATCH v3 0/2] sched/tracing: sched_switch prev_state reported as TASK_RUNNING when it's not Valentin Schneider
2022-01-20 16:25 ` [PATCH v3 1/2] sched/tracing: Don't re-read p->state when emitting sched_switch event Valentin Schneider
2022-03-01 15:24 ` [tip: sched/core] " tip-bot2 for Valentin Schneider
2022-03-04 16:13 ` Valentin Schneider
2022-03-08 18:02 ` Qais Yousef
2022-03-08 18:10 ` Greg KH
2022-03-08 18:51 ` Qais Yousef
2022-04-09 23:38 ` Qais Yousef
2022-04-10 22:06 ` Qais Yousef
2022-04-10 23:22 ` Holger Hoffstätte
2022-04-11 7:18 ` Holger Hoffstätte
2022-04-11 7:28 ` Greg KH
2022-04-11 8:05 ` Holger Hoffstätte
2022-04-11 13:23 ` Greg KH
2022-04-11 13:22 ` Greg KH
2022-04-11 21:06 ` Qais Yousef
2022-01-20 16:25 ` [PATCH v3 2/2] sched/tracing: Report TASK_RTLOCK_WAIT tasks as TASK_UNINTERRUPTIBLE Valentin Schneider
2022-03-01 15:24 ` [tip: sched/core] " tip-bot2 for Valentin Schneider
2022-04-09 23:42 ` [PATCH v3 2/2] " Qais Yousef
2022-04-10 6:14 ` Greg KH
2022-04-10 22:13 ` Qais Yousef
2022-04-11 13:20 ` Greg KH
2022-04-11 20:18 ` Qais Yousef
2022-01-21 17:15 ` Steven Rostedt [this message]
2022-02-27 15:33 ` [PATCH v3 0/2] sched/tracing: sched_switch prev_state reported as TASK_RUNNING when it's not Peter Zijlstra
2022-04-21 22:12 ` [PATCH] sched/tracing: append prev_state to tp args instead Delyan Kratunov
2022-04-22 10:13 ` Valentin Schneider
2022-04-22 11:09 ` Peter Zijlstra
2022-04-22 15:55 ` Steven Rostedt
2022-04-22 16:54 ` Andrii Nakryiko
2022-04-22 16:37 ` Andrii Nakryiko
2022-04-22 17:22 ` Delyan Kratunov
2022-04-22 18:30 ` Alexei Starovoitov
2022-04-26 12:28 ` Peter Zijlstra
2022-04-26 14:09 ` Qais Yousef
2022-04-26 15:54 ` Andrii Nakryiko
2022-04-27 10:34 ` Qais Yousef
2022-04-27 18:17 ` Andrii Nakryiko
2022-04-27 20:32 ` Alexei Starovoitov
2022-04-28 10:02 ` Qais Yousef
2022-05-09 19:32 ` Andrii Nakryiko
2022-05-10 7:01 ` Peter Zijlstra
2022-05-10 8:29 ` Peter Zijlstra
2022-05-10 14:31 ` Steven Rostedt
2022-05-11 18:28 ` [PATCH v2] " Delyan Kratunov
2022-05-11 19:10 ` Steven Rostedt
2022-05-11 22:45 ` [tip: sched/urgent] sched/tracing: Append " tip-bot2 for Delyan Kratunov
2022-05-11 23:40 ` [PATCH v2] sched/tracing: append " Thomas Gleixner
2022-04-26 15:51 ` [PATCH] " Andrii Nakryiko
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