Received-SPF: pass (google.com: domain of linux-kernel+bounces-77335-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Precedence: bulk
MIME-Version: 1.0
References: <20240222051253.1361002-1-jstultz@google.com> <8734tkfrzz.ffs@tglx>
 <CANDhNCoHqX9fo5e=K7_74YSmV8-T2tE-Obu+phhqy+n2bqc4QQ@mail.gmail.com> <87wmqwz1bz.fsf@jogness.linutronix.de>
In-Reply-To: <87wmqwz1bz.fsf@jogness.linutronix.de>
From: John Stultz <jstultz@google.com>
Date: Thu, 22 Feb 2024 12:47:38 -0800
Message-ID: <CANDhNCrWjPL4zW4=uRcFJNFZX6zxC9_GM0uQcNJ=WC9Q6ZS-ag@mail.gmail.com>
Subject: Re: [RFC][PATCH] hrtimer: Use printk_deferred_once for
 hrtimer_interrupt message
To: John Ogness <jogness@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>, LKML <linux-kernel@vger.kernel.org>, 
	Frederic Weisbecker <frederic@kernel.org>, Steven Rostedt <rostedt@goodmis.org>, kernel-team@android.com
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Thu, Feb 22, 2024 at 12:33=E2=80=AFPM John Ogness <jogness@linutronix.de=
> wrote:
> On 2024-02-22, John Stultz <jstultz@google.com> wrote:
> > On Thu, Feb 22, 2024 at 7:17=E2=80=AFAM Thomas Gleixner <tglx@linutroni=
x.de> wrote:
> >> On Wed, Feb 21 2024 at 21:12, John Stultz wrote:
> >> > With qemu, I constantly see lockdep warnings after the
> >> > hrimter_interrupt message is printed:
> >> >
> >> > [   43.434557] hrtimer: interrupt took 6517564 ns
> >> > [   43.435000]
> >> > [   43.435000] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> >> > [   43.435000] [ BUG: Invalid wait context ]
> >>
> >> Do you have PROVE_RAW_LOCK_NESTING enabled?
> >
> > Yes, I do. Let me know if there's anything else you'd like me to try.
>
> This option is to "ensure that the lock nesting rules for PREEMPT_RT
> enabled kernels are not violated."
>
> Since you are not running a PREEMPT_RT enabled kernel, these warnings
> are irrelevant for _your_ kernel.

Ah, mostly I've been running with all the lockdep options as part of
my development of proxy-exec series, as I want to avoid accidentally
introducing any new problems with my work.

> >> > I thought the new printk work was going to resolve this, but
> >> > apparently not
>
> Yes, it will, but it is not all mainline yet. The full printk rework is
> only available as part of the PREEMPT_RT patch series [0]. With that

Ah, my apologies! I know the printk changes are *very* eagerly
awaited, but I haven't been following it closely, and at plumbers I
had the mistaken sense that the key parts had been queued to be merged
in 6.8.

> If you really want to test lock nesting for PREEMPT_RT, I recommend
> applying the PREEMPT_RT series and keeping PROVE_RAW_LOCK_NESTING
> enabled. Otherwise, if you do not want to apply the PREEMPT_RT series, I
> recommend disabling PROVE_RAW_LOCK_NESTING.
>

Ok, will do.  Though would it make sense to hide
PROVE_RAW_LOCK_NESTING under BROKEN or something upstream in the
meantime?

Thanks so much for the response and your efforts on the printk improvements=
!
-john