Commit 4cc3ec3d authored Apr 17, 2026 by Cássio Gabriel Committed by Takashi Iwai Apr 20, 2026

ALSA: als4000: Fix capture trigger chip->mode race



snd_als4000_capture_trigger() updates chip->mode under mixer_lock,
while snd_als4000_set_rate() and snd_als4000_playback_trigger()
serialize the same rate-lock state with reg_lock.

The PCM core serializes callbacks only per acted-on substream, or for an
explicitly linked group, so unlinked playback and capture streams can
run concurrently.

That leaves two races on ALS4000 rate-lock state:
- playback and capture trigger callbacks can concurrently update
  chip->mode and lose one of the SB_RATE_LOCK bits
- snd_als4000_set_rate() can observe chip->mode without the capture
  lock bit set and reprogram the shared sample rate while capture is
  being started

Fix this by taking reg_lock as the outer lock in
snd_als4000_capture_trigger() and nesting mixer_lock only for the CR1E
write. This keeps chip->mode serialized with the rest of the ALS4000
rate-lock users while preserving the existing CR1E programming
sequence.

Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>
Link: https://patch.msgid.link/20260417-als4000-capture-trigger-race-v1-1-daeffc2feb67@gmail.com


Signed-off-by: Takashi Iwai <tiwai@suse.de>

parent 8146cd33

sound/pci/als4000.c

+20 −24

Original line number	Diff line number	Diff line
		@@ -422,13 +422,8 @@ static int snd_als4000_capture_trigger(struct snd_pcm_substream *substream, int
		struct snd_sb *chip = snd_pcm_substream_chip(substream);
		int result = 0;

		/* FIXME race condition in here!!!
		chip->mode non-atomic update gets consistently protected
		by reg_lock always, _except_ for this place!!
		Probably need to take reg_lock as outer (or inner??) lock, too.
		(or serialize both lock operations? probably not, though... - racy?)
		*/
		guard(spinlock)(&chip->mixer_lock);
		guard(spinlock)(&chip->reg_lock);
		scoped_guard(spinlock, &chip->mixer_lock) {
		switch (cmd) {
		case SNDRV_PCM_TRIGGER_START:
		case SNDRV_PCM_TRIGGER_RESUME:
		@@ -446,6 +441,7 @@ static int snd_als4000_capture_trigger(struct snd_pcm_substream *substream, int
		result = -EINVAL;
		break;
		}
		}
		return result;
		}