[PATCH v14 04/12] ALSA: virtio: Propagate PCM send failures through ACK

[Joonho Lee <mynameisjune111@gmail.com>]

virtsnd_pcm_msg_send() can fail while queueing a transfer. Restore the
failed message's length and notify the device about earlier messages
queued by the same call, so they do not remain stranded.

Propagate errors through the indirect transfer callback and commit its
private cursor only after successful submission. Genuine transfer errors
arm stop_operating and return -EPIPE so ALSA can retire the stream.

Close ACK admission under the PCM stream lock before sleeping teardown.
Keep the prepared state protected by the substream lock and reject ACK
through prepare and parameter changes. Reopen admission in the reset
callback while the core holds the PCM lock for its pointer rebase.
An ACK racing with teardown returns -EBADFD and preserves stop state.

Keep the polling feature path unchanged.

Fixes: fe981e67568c ("ALSA: virtio: use ack callback")
Assisted-by: LLM
Signed-off-by: Joonho Lee <mynameisjune111@gmail.com>

---
sound/virtio/virtio_pcm.h     |    6 +
 sound/virtio/virtio_pcm_msg.c |   12 ++
 sound/virtio/virtio_pcm_ops.c |  247 +++++++++++++++++++++++++++++++++++++----
 3 files changed, 239 insertions(+), 26 deletions(-)

diff --git a/sound/virtio/virtio_pcm.h b/sound/virtio/virtio_pcm.h
--- a/sound/virtio/virtio_pcm.h
+++ b/sound/virtio/virtio_pcm.h
@@ -33,6 +33,10 @@
  * @xfer_xrun: Data underflow/overflow state (0 - no xrun, 1 - xrun).
  * @stopped: True if the substream is stopped and must be released on the device
  *           side.
+ * @prepared: True after device PREPARE and the core pointer reset succeed;
+ *            protected by @lock.
+ * @preparing: ACK gate through teardown and prepare's core reset;
+ *             protected by @lock.
  * @suspended: True if the substream is suspended and must be reconfigured on
  *             the device side at resume.
  * @msgs: Allocated I/O messages.
@@ -56,6 +60,8 @@
 	bool xfer_enabled;
 	bool xfer_xrun;
 	bool stopped;
+	bool prepared;
+	bool preparing;
 	bool suspended;
 	struct virtio_pcm_msg **msgs;
 	unsigned int nmsgs;
diff --git a/sound/virtio/virtio_pcm_msg.c b/sound/virtio/virtio_pcm_msg.c
--- a/sound/virtio/virtio_pcm_msg.c
+++ b/sound/virtio/virtio_pcm_msg.c
@@ -260,6 +260,18 @@
 				dev_err(&vdev->dev,
 					"SID %u: failed to send I/O message\n",
 					vss->sid);
+				msg->length -= n;
+
+				/*
+				 * Do not leave earlier messages queued without notifying
+				 * the device when a later message could not be added.
+				 */
+				if (msg_count != vss->msg_count &&
+				    !(vss->features &
+				      (1U << VIRTIO_SND_PCM_F_MSG_POLLING)) &&
+				    virtqueue_kick_prepare(vqueue))
+					virtqueue_notify(vqueue);
+
 				return rc;
 			}
 
diff --git a/sound/virtio/virtio_pcm_ops.c b/sound/virtio/virtio_pcm_ops.c
--- a/sound/virtio/virtio_pcm_ops.c
+++ b/sound/virtio/virtio_pcm_ops.c
@@ -97,6 +97,38 @@
 static int virtsnd_pcm_sync_stop(struct snd_pcm_substream *substream);
 
 /**
+ * virtsnd_pcm_close_ack() - Update PCM prepare admission state.
+ * @substream: Kernel ALSA substream.
+ * @preparing: True while driver prepare and the core pointer reset are active.
+ *
+ * Context: Process context.
+ */
+static void virtsnd_pcm_close_ack(struct snd_pcm_substream *substream,
+				  bool preparing)
+{
+	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
+
+	scoped_guard(pcm_stream_lock_irqsave, substream) {
+		guard(spinlock_irqsave)(&vss->lock);
+		vss->prepared = false;
+		vss->xfer_enabled = false;
+		vss->preparing = preparing;
+	}
+}
+
+/* Keep completed RX data valid while RELEASE drains the device queue. */
+static void virtsnd_pcm_block_ack(struct snd_pcm_substream *substream)
+{
+	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
+
+	scoped_guard(pcm_stream_lock_irqsave, substream) {
+		guard(spinlock_irqsave)(&vss->lock);
+		vss->preparing = true;
+		vss->xfer_enabled = false;
+	}
+}
+
+/**
  * virtsnd_pcm_open() - Open the PCM substream.
  * @substream: Kernel ALSA substream.
  *
@@ -115,7 +147,8 @@
 	snd_pcm_hw_constraint_integer(substream->runtime,
 				      SNDRV_PCM_HW_PARAM_PERIODS);
 
-	vss->stopped = !!virtsnd_pcm_msg_pending_num(vss);
+	scoped_guard(spinlock_irqsave, &vss->lock)
+		vss->stopped = !!vss->msg_count;
 	vss->suspended = false;
 
 	/*
@@ -219,6 +252,8 @@
 	struct virtio_device *vdev = vss->snd->vdev;
 	int rc;
 
+	virtsnd_pcm_close_ack(substream, false);
+
 	if (virtsnd_pcm_msg_pending_num(vss)) {
 		dev_err(&vdev->dev, "SID %u: invalid I/O queue state\n",
 			vss->sid);
@@ -254,6 +289,8 @@
 {
 	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
 
+	virtsnd_pcm_close_ack(substream, false);
+
 	/* If the queue is flushed, we can safely free the messages here. */
 	if (!virtsnd_pcm_msg_pending_num(vss))
 		virtsnd_pcm_msg_free(vss);
@@ -262,17 +299,18 @@
 }
 
 /**
- * virtsnd_pcm_prepare() - Prepare the PCM substream.
+ * virtsnd_pcm_prepare_device() - Prepare the PCM substream on the device.
  * @substream: Kernel ALSA substream.
  *
  * Context: Process context.
  * Return: 0 on success, -errno on failure.
  */
-static int virtsnd_pcm_prepare(struct snd_pcm_substream *substream)
+static int virtsnd_pcm_prepare_device(struct snd_pcm_substream *substream)
 {
 	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
 	struct virtio_device *vdev = vss->snd->vdev;
 	struct virtio_snd_msg *msg;
+	int rc;
 
 	if (!vss->suspended) {
 		if (virtsnd_pcm_msg_pending_num(vss)) {
@@ -287,16 +325,14 @@
 		struct snd_pcm_runtime *runtime = substream->runtime;
 		unsigned int buffer_bytes = snd_pcm_lib_buffer_bytes(substream);
 		unsigned int period_bytes = snd_pcm_lib_period_bytes(substream);
-		int rc;
 
 		rc = virtsnd_pcm_dev_set_params(vss, buffer_bytes, period_bytes,
-						runtime->channels,
-						runtime->format, runtime->rate);
+						 runtime->channels,
+						 runtime->format, runtime->rate);
 		if (rc)
 			return rc;
 	}
 
-	vss->xfer_xrun = false;
 	vss->suspended = false;
 	vss->msg_count = 0;
 	virtsnd_pcm_msg_reset(vss);
@@ -311,7 +347,26 @@
 	if (!msg)
 		return -ENOMEM;
 
-	return virtsnd_ctl_msg_send_sync(vss->snd, msg);
+	rc = virtsnd_ctl_msg_send_sync(vss->snd, msg);
+	if (rc)
+		return rc;
+
+	scoped_guard(spinlock_irqsave, &vss->lock) {
+		vss->xfer_xrun = false;
+	}
+	return 0;
+}
+
+/* Keep ACK closed through the core's locked pointer reset. */
+static int virtsnd_pcm_prepare(struct snd_pcm_substream *substream)
+{
+	int rc;
+
+	virtsnd_pcm_close_ack(substream, true);
+	rc = virtsnd_pcm_prepare_device(substream);
+	if (rc)
+		virtsnd_pcm_close_ack(substream, false);
+	return rc;
 }
 
 /**
@@ -338,6 +393,8 @@
 
 		scoped_guard(spinlock_irqsave, &queue->lock) {
 			guard(spinlock)(&vss->lock);
+			if (vss->preparing || !vss->prepared)
+				return -EBADFD;
 			if (vss->direction == SNDRV_PCM_STREAM_CAPTURE)
 				rc = virtsnd_pcm_msg_send(vss, 0, vss->buffer_bytes);
 			if (rc)
@@ -356,10 +413,12 @@
 
 		return virtsnd_ctl_msg_send_sync(snd, msg);
 	case SNDRV_PCM_TRIGGER_SUSPEND:
-		vss->suspended = true;
+		scoped_guard(spinlock_irqsave, &vss->lock)
+			vss->suspended = true;
 		fallthrough;
 	case SNDRV_PCM_TRIGGER_STOP:
-		vss->stopped = true;
+		scoped_guard(spinlock_irqsave, &vss->lock)
+			vss->stopped = true;
 		fallthrough;
 	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
 		scoped_guard(spinlock_irqsave, &vss->lock) {
@@ -393,11 +452,16 @@
 	struct virtio_snd *snd = vss->snd;
 	struct virtio_snd_msg *msg;
 	unsigned int js = msecs_to_jiffies(virtsnd_msg_timeout_ms);
+	bool stopped;
 	int rc;
 
+	virtsnd_pcm_block_ack(substream);
+
 	cancel_work_sync(&vss->elapsed_period);
 
-	if (!vss->stopped)
+	scoped_guard(spinlock_irqsave, &vss->lock)
+		stopped = vss->stopped;
+	if (!stopped)
 		return 0;
 
 	msg = virtsnd_pcm_ctl_msg_alloc(vss, VIRTIO_SND_R_PCM_RELEASE,
@@ -425,7 +489,8 @@
 		return !rc ? -ETIMEDOUT : rc;
 	}
 
-	vss->stopped = false;
+	scoped_guard(spinlock_irqsave, &vss->lock)
+		vss->stopped = false;
 
 	return 0;
 }
@@ -442,6 +507,10 @@
 virtsnd_pcm_pb_pointer(struct snd_pcm_substream *substream)
 {
 	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
+
+	scoped_guard(spinlock_irqsave, &vss->lock)
+		if (vss->xfer_xrun)
+			return SNDRV_PCM_POS_XRUN;
 
 	return snd_pcm_indirect_playback_pointer(substream,
 		&vss->pcm_indirect,
@@ -461,41 +530,165 @@
 {
 	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
 
+	scoped_guard(spinlock_irqsave, &vss->lock)
+		if (vss->xfer_xrun)
+			return SNDRV_PCM_POS_XRUN;
+
 	return snd_pcm_indirect_capture_pointer(substream,
 		&vss->pcm_indirect,
 		vss->hw_ptr);
 }
 
+struct virtsnd_pcm_transfer {
+	struct snd_pcm_indirect indirect;
+	int error;
+};
+
 static void virtsnd_pcm_trans_copy(struct snd_pcm_substream *substream,
 				   struct snd_pcm_indirect *rec, size_t bytes)
 {
 	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
-
-	virtsnd_pcm_msg_send(vss, rec->sw_data, bytes);
+	struct virtsnd_pcm_transfer *transfer =
+		container_of(rec, struct virtsnd_pcm_transfer, indirect);
+
+	if (transfer->error)
+		return;
+
+	transfer->error = virtsnd_pcm_msg_send(vss, rec->sw_data, bytes);
+}
+
+/* Caller holds vss->lock. */
+static void virtsnd_pcm_transfer_failed(struct virtio_pcm_substream *vss)
+{
+	vss->xfer_enabled = false;
+	vss->stopped = true;
+	vss->substream->runtime->stop_operating = true;
+}
+
+/* The caller holds the PCM lock, also used by DROP and state transitions. */
+static int virtsnd_pcm_ack_state(struct snd_pcm_substream *substream)
+{
+	switch (substream->runtime->state) {
+	case SNDRV_PCM_STATE_XRUN:
+		return -EPIPE;
+	case SNDRV_PCM_STATE_PREPARED:
+	case SNDRV_PCM_STATE_RUNNING:
+	case SNDRV_PCM_STATE_PAUSED:
+	case SNDRV_PCM_STATE_DRAINING:
+		if (atomic_read(&substream->runtime->buffer_accessing) < 0)
+			return -EBADFD;
+		return 0;
+	default:
+		return -EBADFD;
+	}
 }
 
 static int virtsnd_pcm_pb_ack(struct snd_pcm_substream *substream)
 {
 	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
 	struct virtio_snd_queue *queue = virtsnd_pcm_queue(vss);
-
-	guard(spinlock_irqsave)(&queue->lock);
-	guard(spinlock)(&vss->lock);
-
-	return snd_pcm_indirect_playback_transfer(substream, &vss->pcm_indirect,
-						  virtsnd_pcm_trans_copy);
+	struct virtsnd_pcm_transfer transfer = {};
+	int rc;
+
+	rc = virtsnd_pcm_ack_state(substream);
+	if (rc)
+		return rc;
+
+	scoped_guard(spinlock_irqsave, &queue->lock) {
+		guard(spinlock)(&vss->lock);
+		if (vss->preparing || !vss->prepared)
+			return -EBADFD;
+		if (vss->stopped && !vss->xfer_xrun)
+			return -EBADFD;
+		if (vss->xfer_xrun) {
+			rc = -EPIPE;
+		} else {
+			transfer.indirect = vss->pcm_indirect;
+			rc = snd_pcm_indirect_playback_transfer(substream,
+							       &transfer.indirect,
+							       virtsnd_pcm_trans_copy);
+			if (!rc)
+				rc = transfer.error;
+		}
+		if (rc)
+			virtsnd_pcm_transfer_failed(vss);
+		else
+			vss->pcm_indirect = transfer.indirect;
+	}
+	if (rc) {
+		dev_err(&vss->snd->vdev->dev,
+			"SID %u: playback ACK transfer failed: %d\n",
+			vss->sid, rc);
+		return -EPIPE;
+	}
+
+	return 0;
 }
 
 static int virtsnd_pcm_cp_ack(struct snd_pcm_substream *substream)
 {
 	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
 	struct virtio_snd_queue *queue = virtsnd_pcm_queue(vss);
-
-	guard(spinlock_irqsave)(&queue->lock);
-	guard(spinlock)(&vss->lock);
-
-	return snd_pcm_indirect_capture_transfer(substream, &vss->pcm_indirect,
-						 virtsnd_pcm_trans_copy);
+	struct virtsnd_pcm_transfer transfer = {};
+	int rc;
+
+	rc = virtsnd_pcm_ack_state(substream);
+	if (rc)
+		return rc;
+
+	scoped_guard(spinlock_irqsave, &queue->lock) {
+		guard(spinlock)(&vss->lock);
+		if (vss->preparing || !vss->prepared)
+			return -EBADFD;
+		if (vss->stopped && !vss->xfer_xrun &&
+		    substream->runtime->state != SNDRV_PCM_STATE_DRAINING)
+			return -EBADFD;
+		if (vss->xfer_xrun) {
+			rc = -EPIPE;
+		} else {
+			transfer.indirect = vss->pcm_indirect;
+			rc = snd_pcm_indirect_capture_transfer(substream,
+							       &transfer.indirect,
+							       virtsnd_pcm_trans_copy);
+			if (!rc)
+				rc = transfer.error;
+		}
+		if (rc)
+			virtsnd_pcm_transfer_failed(vss);
+		else
+			vss->pcm_indirect = transfer.indirect;
+	}
+	if (rc) {
+		dev_err(&vss->snd->vdev->dev,
+			"SID %u: capture ACK transfer failed: %d\n",
+			vss->sid, rc);
+		return -EPIPE;
+	}
+
+	return 0;
+}
+
+/**
+ * virtsnd_pcm_reset() - Reset PCM pointers and complete prepare admission.
+ * @substream: Kernel ALSA substream.
+ *
+ * Context: PCM stream lock held.
+ * Return: 0 on success, -errno on failure.
+ */
+static int virtsnd_pcm_reset(struct snd_pcm_substream *substream)
+{
+	struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
+	int rc;
+
+	rc = snd_pcm_lib_reset(substream);
+	scoped_guard(spinlock_irqsave, &vss->lock) {
+		if (vss->preparing) {
+			vss->prepared = !rc;
+			vss->preparing = false;
+		}
+	}
+
+	return rc;
 }
 
 /* PCM substream operators map. */
@@ -507,6 +700,7 @@
 		.hw_params = virtsnd_pcm_hw_params,
 		.hw_free = virtsnd_pcm_hw_free,
 		.prepare = virtsnd_pcm_prepare,
+		.reset = virtsnd_pcm_reset,
 		.trigger = virtsnd_pcm_trigger,
 		.sync_stop = virtsnd_pcm_sync_stop,
 		.pointer = virtsnd_pcm_pb_pointer,
@@ -519,6 +713,7 @@
 		.hw_params = virtsnd_pcm_hw_params,
 		.hw_free = virtsnd_pcm_hw_free,
 		.prepare = virtsnd_pcm_prepare,
+		.reset = virtsnd_pcm_reset,
 		.trigger = virtsnd_pcm_trigger,
 		.sync_stop = virtsnd_pcm_sync_stop,
 		.pointer = virtsnd_pcm_cp_pointer,