linux-kernel - Re: [PATCH] Revert "gpio: mpc8xxx: change the gpio interrupt flags."

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Date:   Wed, 21 Jul 2021 22:25:33 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     Song Hui <hui.song_1@....com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        stable@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "gpio: mpc8xxx: change the gpio interrupt flags."

On Fri, Jul 02 2021 at 15:37, Rasmus Villemoes wrote:
> This reverts commit 3d5bfbd9716318b1ca5c38488aa69f64d38a9aa5.
>
> When booting with threadirqs, it causes a splat
>
>   WARNING: CPU: 0 PID: 29 at kernel/irq/handle.c:159 __handle_irq_event_percpu+0x1ec/0x27c
>   irq 66 handler irq_default_primary_handler+0x0/0x1c enabled interrupts
>
> That splat later went away with commit 81e2073c175b ("genirq: Disable
> interrupts for force threaded handlers"), which got backported to
> -stable. However, when running an -rt kernel, the splat still
> exists. Moreover, quoting Thomas Gleixner [1]
>
>   But 3d5bfbd97163 ("gpio: mpc8xxx: change the gpio interrupt flags.")
>   has nothing to do with that:
>
>       "Delete the interrupt IRQF_NO_THREAD flags in order to gpio interrupts
>        can be threaded to allow high-priority processes to preempt."
>
>   This changelog is blatantly wrong. In mainline forced irq threads
>   have always been invoked with softirqs disabled, which obviously
>   makes them non-preemptible.
>
> So the patch didn't even do what its commit log said.
>
> [1] https://lore.kernel.org/lkml/871r8zey88.ffs@nanos.tec.linutronix.de/
>
> Cc: stable@...r.kernel.org # v5.9+
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
> Thomas, please correct me if I misinterpreted your explanation.

Nothing to correct here.

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>