[RFC PATCH v3 2/2] ALSA: pcm: refresh capture pointers in the drain action
From: Joonho Lee
Date: Wed Oct 14 2026 - 11:27:13 EST
Capture drain decides whether to retain unread data from the cached
hardware pointer. A final subperiod can be omitted if the driver has
advanced without a period notification or another pointer query.
Refresh each running capture pointer in snd_pcm_do_drain_init(), with
the normal drain action holding the stream and linked-group locks.
Allow pointer accounting to return an error without issuing a nested
XRUN or drain-complete action. Guard both the driver XRUN sentinel and
the stop-threshold path; otherwise a linked drain can recursively enter
the group stop action while its member locks are held.
Let drain init own the stop: an update error ends that member in SETUP,
while a successful update retains available capture frames in DRAINING.
Ordinary pointer queries and period notifications retain their existing
XRUN and drain-completion actions.
Suggested-by: Takashi Iwai <tiwai@xxxxxxx>
Link: https://lore.kernel.org/all/8733u8g0kh.wl-tiwai@xxxxxxx/
Link: https://lore.kernel.org/all/87y0c0el29.wl-tiwai@xxxxxxx/
Assisted-by: LLM
Signed-off-by: Joonho Lee <mynameisjune111@xxxxxxxxx>
---
sound/core/pcm_lib.c | 34 ++++++++++++++++++++++++----------
sound/core/pcm_local.h | 2 ++
sound/core/pcm_native.c | 10 ++++++++--
3 files changed, 34 insertions(+), 12 deletions(-)
diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index de952f639d3b..2bb24d7dd2a1 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -206,8 +206,9 @@ void __snd_pcm_xrun(struct snd_pcm_substream *substream)
#endif
-int snd_pcm_update_state(struct snd_pcm_substream *substream,
- struct snd_pcm_runtime *runtime)
+static int do_pcm_update_state(struct snd_pcm_substream *substream,
+ struct snd_pcm_runtime *runtime,
+ bool notify)
{
snd_pcm_uframes_t avail;
@@ -216,12 +217,14 @@ int snd_pcm_update_state(struct snd_pcm_substream *substream,
runtime->avail_max = avail;
if (runtime->state == SNDRV_PCM_STATE_DRAINING) {
if (avail >= runtime->buffer_size) {
- snd_pcm_drain_done(substream);
+ if (notify)
+ snd_pcm_drain_done(substream);
return -EPIPE;
}
} else {
if (avail >= runtime->stop_threshold) {
- __snd_pcm_xrun(substream);
+ if (notify)
+ __snd_pcm_xrun(substream);
return -EPIPE;
}
}
@@ -233,6 +236,12 @@ int snd_pcm_update_state(struct snd_pcm_substream *substream,
return 0;
}
+int snd_pcm_update_state(struct snd_pcm_substream *substream,
+ struct snd_pcm_runtime *runtime)
+{
+ return do_pcm_update_state(substream, runtime, true);
+}
+
static void update_audio_tstamp(struct snd_pcm_substream *substream,
struct timespec64 *curr_tstamp,
struct timespec64 *audio_tstamp)
@@ -283,8 +292,12 @@ static void update_audio_tstamp(struct snd_pcm_substream *substream,
runtime->driver_tstamp = driver_tstamp;
}
-static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
- unsigned int in_interrupt)
+/*
+ * Call with the stream lock held. With notify=false the caller handles
+ * stopping the stream, so pointer errors must not start a nested action.
+ */
+int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
+ bool in_interrupt, bool notify)
{
struct snd_pcm_runtime *runtime = substream->runtime;
snd_pcm_uframes_t pos;
@@ -322,7 +335,8 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
}
if (pos == SNDRV_PCM_POS_XRUN) {
- __snd_pcm_xrun(substream);
+ if (notify)
+ __snd_pcm_xrun(substream);
return -EPIPE;
}
if (pos >= runtime->buffer_size) {
@@ -490,13 +504,13 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
update_audio_tstamp(substream, &curr_tstamp, &audio_tstamp);
- return snd_pcm_update_state(substream, runtime);
+ return do_pcm_update_state(substream, runtime, notify);
}
/* CAUTION: call it with irq disabled */
int snd_pcm_update_hw_ptr(struct snd_pcm_substream *substream)
{
- return snd_pcm_update_hw_ptr0(substream, 0);
+ return snd_pcm_update_hw_ptr0(substream, false, true);
}
/**
@@ -1906,7 +1920,7 @@ void snd_pcm_period_elapsed_under_stream_lock(struct snd_pcm_substream *substrea
runtime = substream->runtime;
if (!snd_pcm_running(substream) ||
- snd_pcm_update_hw_ptr0(substream, 1) < 0)
+ snd_pcm_update_hw_ptr0(substream, true, true) < 0)
goto _end;
#ifdef CONFIG_SND_PCM_TIMER
diff --git a/sound/core/pcm_local.h b/sound/core/pcm_local.h
index ecb21697ae3a..12bb6e75329a 100644
--- a/sound/core/pcm_local.h
+++ b/sound/core/pcm_local.h
@@ -28,6 +28,8 @@ int pcm_lib_apply_appl_ptr(struct snd_pcm_substream *substream,
int snd_pcm_update_state(struct snd_pcm_substream *substream,
struct snd_pcm_runtime *runtime);
int snd_pcm_update_hw_ptr(struct snd_pcm_substream *substream);
+int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
+ bool in_interrupt, bool notify);
void snd_pcm_playback_silence(struct snd_pcm_substream *substream,
snd_pcm_uframes_t new_hw_ptr);
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index defbb2977efe..91ae46de3521 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -2094,6 +2094,8 @@ static int snd_pcm_do_drain_init(struct snd_pcm_substream *substream,
snd_pcm_state_t state)
{
struct snd_pcm_runtime *runtime = substream->runtime;
+ int err;
+
if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
switch (runtime->state) {
case SNDRV_PCM_STATE_PREPARED:
@@ -2119,8 +2121,12 @@ static int snd_pcm_do_drain_init(struct snd_pcm_substream *substream,
if (runtime->state == SNDRV_PCM_STATE_RUNNING) {
snd_pcm_state_t new_state;
- new_state = snd_pcm_capture_avail(runtime) > 0 ?
- SNDRV_PCM_STATE_DRAINING : SNDRV_PCM_STATE_SETUP;
+ err = snd_pcm_update_hw_ptr0(substream, false, false);
+ if (err < 0)
+ new_state = SNDRV_PCM_STATE_SETUP;
+ else
+ new_state = snd_pcm_capture_avail(runtime) > 0 ?
+ SNDRV_PCM_STATE_DRAINING : SNDRV_PCM_STATE_SETUP;
snd_pcm_do_stop(substream, new_state);
snd_pcm_post_stop(substream, new_state);
}
--
2.54.0 (Apple Git-157)