[PATCH v7 15/16] ALSA: pcm: synchronize stopped paused streams

[Joonho Lee <mynameisjune111@gmail.com>]

A paused stream can still own DMA requests even though snd_pcm_running()
returns false. Stopping that stream without marking stop_operating lets
a subsequent prepare skip sync_stop and encounter outstanding requests.

Mark a paused stream for synchronous stop when snd_pcm_do_stop() handles
its actual stop transition. This also covers paused XRUN cleanup without
having the driver predict a stop from an intermediate ACK position.

The non-staged virtio-snd partial-read test previously failed its first
prepare with -EBADFD. With the companion driver changes it prepares and
captures 48000 frames. Playback pause/drop/prepare/write and reopen tests
also pass under ARM64 QEMU with KASAN and lockdep.

This changes the core stop path for paused PCM streams beyond virtio-snd.
Coverage does not extend to all PCM drivers.

Assisted-by: LLM
Signed-off-by: Joonho Lee <mynameisjune111@gmail.com>
---
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index a2ea44c..ac2e5c2 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -1611,6 +1611,9 @@ static int snd_pcm_do_stop(struct snd_pcm_substream *substream,
 		substream->ops->trigger(substream, SNDRV_PCM_TRIGGER_STOP);
 		substream->runtime->stop_operating = true;
 	}
+	/* Paused DMA can still own requests which sync_stop must drain. */
+	if (substream->runtime->state == SNDRV_PCM_STATE_PAUSED)
+		substream->runtime->stop_operating = true;
 	return 0; /* unconditionally stop all substreams */
 }