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

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Message-Id: <20210702133712.128611-1-linux@rasmusvillemoes.dk>
Date:   Fri,  2 Jul 2021 15:37:12 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        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: [PATCH] Revert "gpio: mpc8xxx: change the gpio interrupt flags."

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.

 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