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ASoC: meson: axg-fifo: fix irq scheduling issue with PREEMPT_RT

Message ID 20240806102707.3825703-1-jbrunet@baylibre.com
State New
Headers show
Series ASoC: meson: axg-fifo: fix irq scheduling issue with PREEMPT_RT | expand

Commit Message

Jerome Brunet Aug. 6, 2024, 10:27 a.m. UTC
With PREEMPT_RT enabled, spinlocks become preemptible.
This is usually not a problem with spinlocks used in IRQ context since
IRQ handlers get threaded. However, if IRQF_ONESHOT is set, the upper half
of a threaded irq handler won't be threaded and this causes scheduling
problems if spinlocks are used in the upper half, like with regmap when
'.fast_io' is set.

In this particular instance, it is actually better to do everything in
the bottom half 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(-)

Comments

Mark Brown Aug. 13, 2024, 2:43 p.m. UTC | #1
On Tue, 06 Aug 2024 12:27:03 +0200, Jerome Brunet wrote:
> With PREEMPT_RT enabled, spinlocks become preemptible.
> This is usually not a problem with spinlocks used in IRQ context since
> IRQ handlers get threaded. However, if IRQF_ONESHOT is set, the upper half
> of a threaded irq handler won't be threaded and this causes scheduling
> problems if spinlocks are used in the upper half, like with regmap when
> '.fast_io' is set.
> 
> [...]

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
Sebastian Andrzej Siewior Aug. 13, 2024, 3:22 p.m. UTC | #2
On 2024-08-13 15:43:54 [+0100], Mark Brown wrote:
> On Tue, 06 Aug 2024 12:27:03 +0200, Jerome Brunet wrote:
> > With PREEMPT_RT enabled, spinlocks become preemptible.
> > This is usually not a problem with spinlocks used in IRQ context since
> > IRQ handlers get threaded. However, if IRQF_ONESHOT is set, the upper half
> > of a threaded irq handler won't be threaded and this causes scheduling
> > problems if spinlocks are used in the upper half, like with regmap when
> > '.fast_io' is set.
> > 
> > [...]
> 
> 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

Didn't you already apply v2 of this?

Sebastian
Mark Brown Aug. 13, 2024, 5:03 p.m. UTC | #3
On Tue, Aug 13, 2024 at 05:22:43PM +0200, Sebastian Andrzej Siewior wrote:
> On 2024-08-13 15:43:54 [+0100], Mark Brown wrote:

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

> Didn't you already apply v2 of this?

Perhaps?  There's a decent chance my copy of b4 just didn't spot a
difference between the two versions and acked both.
diff mbox series

Patch

diff --git a/sound/soc/meson/axg-fifo.c b/sound/soc/meson/axg-fifo.c
index 7e6090af720b..d0d05fa44d66 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 bottom half of a threaded irq 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;