Re: [PATCH v3 2/2] sched/tracing: Report TASK_RTLOCK_WAIT tasks as TASK_UNINTERRUPTIBLE

From: Qais Yousef <qais.yousef@arm.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: stable@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Abhijeet Dharmapurikar" <adharmap@quicinc.com>,
	"Dietmar Eggemann" <dietmar.eggemann@arm.com>,
	"Steven Rostedt" <rostedt@goodmis.org>,
	"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>,
	"Valentin Schneider" <valentin.schneider@arm.com>
Subject: Re: [PATCH v3 2/2] sched/tracing: Report TASK_RTLOCK_WAIT tasks as TASK_UNINTERRUPTIBLE
Date: Sun, 10 Apr 2022 23:13:25 +0100	[thread overview]
Message-ID: <20220410221325.fimxzpzg26zmmsiz@airbuntu> (raw)
In-Reply-To: <YlJ1q0zohdPvQBUd@kroah.com>

On 04/10/22 08:14, Greg KH wrote:
> On Sun, Apr 10, 2022 at 12:42:24AM +0100, Qais Yousef wrote:
> > +CC stable
> > 
> > On 01/20/22 16:25, Valentin Schneider wrote:
> > > TASK_RTLOCK_WAIT currently isn't part of TASK_REPORT, thus a task blocking
> > > on an rtlock will appear as having a task state == 0, IOW TASK_RUNNING.
> > > 
> > > The actual state is saved in p->saved_state, but reading it after reading
> > > p->__state has a few issues:
> > > o that could still be TASK_RUNNING in the case of e.g. rt_spin_lock
> > > o ttwu_state_match() might have changed that to TASK_RUNNING
> > > 
> > > As pointed out by Eric, adding TASK_RTLOCK_WAIT to TASK_REPORT implies
> > > exposing a new state to userspace tools which way not know what to do with
> > > them. The only information that needs to be conveyed here is that a task is
> > > waiting on an rt_mutex, which matches TASK_UNINTERRUPTIBLE - there's no
> > > need for a new state.
> > > 
> > > Reported-by: Uwe Kleine-Kï¿½nig <u.kleine-koenig@pengutronix.de>
> > > Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> > 
> > Any objection for this to be picked up by stable? We care about Patch 1 only in
> > this series for stable, but it seems sensible to pick this one too, no strong
> > feeling if it is omitted though.
> > 
> > AFAICT it seems the problem dates back since commit:
> > 
> > 	1593baab910d ("sched/debug: Implement consistent task-state printing")
> > 
> > or even before. I think v4.14+ is good enough.
> 
> 
> <formletter>
> 
> This is not the correct way to submit patches for inclusion in the
> stable kernel tree.  Please read:
>     https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> for how to do this properly.
> 
> </formletter>

Apologies.

commit: 25795ef6299f07ce3838f3253a9cb34f64efcfae
Subject: sched/tracing: Report TASK_RTLOCK_WAIT tasks as TASK_UNINTERRUPTIBLE

I am interested in Patch 1 in this series as I know it impacts some Android
5.10 users. But this patch seems a good candidate for stable too since it was
observed by a user (Uwe) and AFAICT the problem dates back to v4.14+ kernels.

Suggested kernels: v4.14+. This has already been picked up by AUTOSEL for
v5.15+ stable trees.

Hope I got the process right this time.

Thanks!

--
Qais Yousef