[PATCH v2] ASoC: meson: axg-fifo: fix irq scheduling issue with PREEMPT_RT

[PATCH v2] ASoC: meson: axg-fifo: fix irq scheduling issue with PREEMPT_RT

[Jerome Brunet]

With PREEMPT_RT enabled a spinlock_t becomes a sleeping lock.

This is usually not a problem with spinlocks used in IRQ context since
IRQ handlers get threaded. However, if IRQF_ONESHOT is set, the primary
handler won't be force-threaded and runs always in hardirq context. This is
a problem because spinlock_t requires a preemptible context on PREEMPT_RT.

In this particular instance, regmap mmio uses spinlock_t to protect the
register access and IRQF_ONESHOT is set on the IRQ. In this case, it is
actually better to do everything in threaded handler and it solves the
problem with PREEMPT_RT.

Reported-by: Arseniy Krasnov <avkrasnov@salutedevices.com>
Closes: https://lore.kernel.org/linux-amlogic/20240729131652.3012327-1-avkrasnov@salutedevices.com
Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Fixes: b11d26660dff ("ASoC: meson: axg-fifo: use threaded irq to check periods")
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
---
 sound/soc/meson/axg-fifo.c | 26 ++++++++++----------------
 1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/sound/soc/meson/axg-fifo.c b/sound/soc/meson/axg-fifo.c
index 7e6090af720b..75909196b769 100644
--- a/sound/soc/meson/axg-fifo.c
+++ b/sound/soc/meson/axg-fifo.c
@@ -207,25 +207,18 @@ static irqreturn_t axg_fifo_pcm_irq_block(int irq, void *dev_id)
 	status = FIELD_GET(STATUS1_INT_STS, status);
 	axg_fifo_ack_irq(fifo, status);
 
-	/* Use the thread to call period elapsed on nonatomic links */
-	if (status & FIFO_INT_COUNT_REPEAT)
-		return IRQ_WAKE_THREAD;
+	if (status & ~FIFO_INT_COUNT_REPEAT)
+		dev_dbg(axg_fifo_dev(ss), "unexpected irq - STS 0x%02x\n",
+			status);
 
-	dev_dbg(axg_fifo_dev(ss), "unexpected irq - STS 0x%02x\n",
-		status);
+	if (status & FIFO_INT_COUNT_REPEAT) {
+		snd_pcm_period_elapsed(ss);
+		return IRQ_HANDLED;
+	}
 
 	return IRQ_NONE;
 }
 
-static irqreturn_t axg_fifo_pcm_irq_block_thread(int irq, void *dev_id)
-{
-	struct snd_pcm_substream *ss = dev_id;
-
-	snd_pcm_period_elapsed(ss);
-
-	return IRQ_HANDLED;
-}
-
 int axg_fifo_pcm_open(struct snd_soc_component *component,
 		      struct snd_pcm_substream *ss)
 {
@@ -251,8 +244,9 @@ int axg_fifo_pcm_open(struct snd_soc_component *component,
 	if (ret)
 		return ret;
 
-	ret = request_threaded_irq(fifo->irq, axg_fifo_pcm_irq_block,
-				   axg_fifo_pcm_irq_block_thread,
+	/* Use the threaded irq handler only with non-atomic links */
+	ret = request_threaded_irq(fifo->irq, NULL,
+				   axg_fifo_pcm_irq_block,
 				   IRQF_ONESHOT, dev_name(dev), ss);
 	if (ret)
 		return ret;
-- 
2.43.0


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Re: [PATCH v2] ASoC: meson: axg-fifo: fix irq scheduling issue with PREEMPT_RT

[Sebastian Andrzej Siewior]

On 2024-08-07 18:27:03 [+0200], Jerome Brunet wrote:
> With PREEMPT_RT enabled a spinlock_t becomes a sleeping lock.
> 
> This is usually not a problem with spinlocks used in IRQ context since
> IRQ handlers get threaded. However, if IRQF_ONESHOT is set, the primary
> handler won't be force-threaded and runs always in hardirq context. This is
> a problem because spinlock_t requires a preemptible context on PREEMPT_RT.
> 
> In this particular instance, regmap mmio uses spinlock_t to protect the
> register access and IRQF_ONESHOT is set on the IRQ. In this case, it is
> actually better to do everything in threaded handler and it solves the
> problem with PREEMPT_RT.
> 
> Reported-by: Arseniy Krasnov <avkrasnov@salutedevices.com>
> Closes: https://lore.kernel.org/linux-amlogic/20240729131652.3012327-1-avkrasnov@salutedevices.com
> Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Fixes: b11d26660dff ("ASoC: meson: axg-fifo: use threaded irq to check periods")
> Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Sebastian

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Re: [PATCH v2] ASoC: meson: axg-fifo: fix irq scheduling issue with PREEMPT_RT

[Mark Brown]

On Wed, 07 Aug 2024 18:27:03 +0200, Jerome Brunet wrote:
> With PREEMPT_RT enabled a spinlock_t becomes a sleeping lock.
> 
> This is usually not a problem with spinlocks used in IRQ context since
> IRQ handlers get threaded. However, if IRQF_ONESHOT is set, the primary
> handler won't be force-threaded and runs always in hardirq context. This is
> a problem because spinlock_t requires a preemptible context on PREEMPT_RT.
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git for-next

Thanks!

[1/1] ASoC: meson: axg-fifo: fix irq scheduling issue with PREEMPT_RT
      commit: 5003d0ce5c7da3a02c0aff771f516f99731e7390

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark


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