linux-kernel - [PATCH] ASoC: meson: axg-fifo: fix irq scheduling issue with PREEMPT

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20240806102707.3825703-1-jbrunet@baylibre.com>
Date: Tue,  6 Aug 2024 12:27:03 +0200
From: Jerome Brunet <jbrunet@...libre.com>
To: Mark Brown <broonie@...nel.org>,
	Liam Girdwood <lgirdwood@...il.com>
Cc: Jerome Brunet <jbrunet@...libre.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	linux-amlogic@...ts.infradead.org,
	alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org,
	Arseniy Krasnov <avkrasnov@...utedevices.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH] ASoC: meson: axg-fifo: fix irq scheduling issue with PREEMPT_RT

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@...utedevices.com>
Closes: https://lore.kernel.org/linux-amlogic/20240729131652.3012327-1-avkrasnov@salutedevices.com
Suggested-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Fixes: b11d26660dff ("ASoC: meson: axg-fifo: use threaded irq to check periods")
Signed-off-by: Jerome Brunet <jbrunet@...libre.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..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;
-- 
2.43.0