linux-kernel - Re: [PATCH v3 2/2] sched/tracing: Report TASK_RTLOCK_WAIT tasks as TASK

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Date:   Mon, 11 Apr 2022 21:18:42 +0100
From:   Qais Yousef <qais.yousef@....com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     stable@...r.kernel.org, linux-kernel@...r.kernel.org,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Abhijeet Dharmapurikar <adharmap@...cinc.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Juri Lelli <juri.lelli@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Alexey Gladkov <legion@...nel.org>,
        "Kenta.Tada@...y.com" <Kenta.Tada@...y.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Ed Tsai <ed.tsai@...iatek.com>,
        Valentin Schneider <valentin.schneider@....com>
Subject: Re: [PATCH v3 2/2] sched/tracing: Report TASK_RTLOCK_WAIT tasks as
 TASK_UNINTERRUPTIBLE

On 04/11/22 15:20, Greg KH wrote:
> On Sun, Apr 10, 2022 at 11:13:25PM +0100, Qais Yousef wrote:
> > 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@...gutronix.de>
> > > > > Signed-off-by: Valentin Schneider <valentin.schneider@....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.
> 
> I do not think you have tested this in any of those kernels, as it
> breaks the build :(
> 
> Please send a set of patches, properly backported and tested, that you
> wish to see applied to stable kernels and we will be glad to review them
> and apply them.  But to suggest patches to be merged that you have not
> even tested is not good.

Okay. Maybe I was trying to chew too much. I care about patch 1 only. I'll make
sure it builds and works against 5.10 and post it separately. Please ignore
this one.

Sorry for the noise.

Thanks

--
Qais Yousef