[PATCH] Revert "gpio: mpc8xxx: change the gpio interrupt flags."

[PATCH] Revert "gpio: mpc8xxx: change the gpio interrupt flags."

[Rasmus Villemoes]

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@vger.kernel.org # v5.9+
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
Thomas, please correct me if I misinterpreted your explanation.

 drivers/gpio/gpio-mpc8xxx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpio/gpio-mpc8xxx.c b/drivers/gpio/gpio-mpc8xxx.c
index 4b9157a69fca..50b321a1ab1b 100644
--- a/drivers/gpio/gpio-mpc8xxx.c
+++ b/drivers/gpio/gpio-mpc8xxx.c
@@ -405,7 +405,7 @@ static int mpc8xxx_probe(struct platform_device *pdev)
 
 	ret = devm_request_irq(&pdev->dev, mpc8xxx_gc->irqn,
 			       mpc8xxx_gpio_irq_cascade,
-			       IRQF_SHARED, "gpio-cascade",
+			       IRQF_NO_THREAD | IRQF_SHARED, "gpio-cascade",
 			       mpc8xxx_gc);
 	if (ret) {
 		dev_err(&pdev->dev,
-- 
2.31.1

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

[Bartosz Golaszewski]

On Fri, Jul 2, 2021 at 3:37 PM Rasmus Villemoes
<linux@rasmusvillemoes.dk> 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@vger.kernel.org # v5.9+
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> ---

Applied for fixes, thanks!

Bartosz

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

[Thomas Gleixner]

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@vger.kernel.org # v5.9+
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> ---
> Thomas, please correct me if I misinterpreted your explanation.

Nothing to correct here.

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