[RFC PATCH 2/2] ALSA: pcm: refresh capture pointers before drain

[Joonho Lee <mynameisjune111@gmail.com>]

Refresh active capture pointers before the drain transition so the final
captured tail is accounted before reads finish.

Assisted-by: LLM
Signed-off-by: Joonho Lee <mynameisjune111@gmail.com>
---
 sound/core/pcm_native.c | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index defbb2977efe..622ae7be2d04 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -2176,14 +2176,32 @@ static int snd_pcm_drain(struct snd_pcm_substream *substream,
 	} else if (substream->f_flags & O_NONBLOCK)
 		nonblock = 1;
 
-	snd_pcm_stream_lock_irq(substream);
-	/* resume pause */
-	if (runtime->state == SNDRV_PCM_STATE_PAUSED)
-		snd_pcm_pause(substream, false);
+	/* Keep linked runtimes alive until the initial drain action completes. */
+	scoped_guard(rwsem_read, &snd_pcm_link_rwsem) {
+		snd_pcm_stream_lock_irq(substream);
+		/* Resume before refreshing capture positions. */
+		if (runtime->state == SNDRV_PCM_STATE_PAUSED)
+			snd_pcm_pause(substream, false);
+		snd_pcm_stream_unlock_irq(substream);
+
+		/* A pointer error may stop the group: hold only this member's lock. */
+		snd_pcm_group_for_each_entry(s, substream) {
+			if (s->stream != SNDRV_PCM_STREAM_CAPTURE)
+				continue;
+			scoped_guard(pcm_stream_lock_irq, s) {
+				if (s->runtime->state == SNDRV_PCM_STATE_RUNNING)
+					result = snd_pcm_update_hw_ptr(s);
+			}
+			if (result < 0)
+				break;
+		}
 
-	/* pre-start/stop - all running streams are changed to DRAINING state */
-	result = snd_pcm_action(&snd_pcm_action_drain_init, substream,
-				ACTION_ARG_IGNORE);
+		snd_pcm_stream_lock_irq(substream);
+		/* Change the stable group to DRAINING only after all refreshes. */
+		if (result >= 0)
+			result = snd_pcm_action(&snd_pcm_action_drain_init,
+						substream, ACTION_ARG_IGNORE);
+	}
 	if (result < 0)
 		goto unlock;
 	/* in non-blocking, we don't wait in ioctl but let caller poll */