One more thing I missed yesterday:

On Mon, 25 Jan 2021, Guennadi Liakhovetski wrote:

On Sun, 24 Jan 2021, Anton Yakovlev wrote:

quoted

Introduce the operators required for the operation of substreams.

Signed-off-by: Anton Yakovlev <anton.yakovlev@opensynergy.com>
---
sound/virtio/Makefile         |   3 +-
sound/virtio/virtio_pcm.c     |   5 +-
sound/virtio/virtio_pcm.h     |   2 +
sound/virtio/virtio_pcm_ops.c | 513 ++++++++++++++++++++++++++++++++++
4 files changed, 521 insertions(+), 2 deletions(-)
create mode 100644 sound/virtio/virtio_pcm_ops.c

[snip]

quoted

diff --git a/sound/virtio/virtio_pcm_ops.c b/sound/virtio/virtio_pcm_ops.c
new file mode 100644
index 000000000000..19882777fcd6
--- /dev/null
+++ b/sound/virtio/virtio_pcm_ops.c

@@ -0,0 +1,513 @@

[snip]

quoted

+/**
+ * virtsnd_pcm_release() - Release the PCM substream on the device side.
+ * @substream: VirtIO substream.
+ *
+ * Context: Any context that permits to sleep.
+ * Return: 0 on success, -errno on failure.
+ */
+static inline bool virtsnd_pcm_released(struct virtio_pcm_substream 
*substream)
+{
+	/*
+	 * The spec states that upon receipt of the RELEASE command "the 
device
+	 * MUST complete all pending I/O messages for the specified stream 
ID".
+	 * Thus, we consider the absence of I/O messages in the queue as an
+	 * indication that the substream has been released.
+	 */
+	return atomic_read(&substream->msg_count) == 0;

Also here having it atomic doesn't really seem to help. This just means, that 
at some point of time it was == 0.

quoted

+}
+
+static int virtsnd_pcm_release(struct virtio_pcm_substream *substream)

kernel-doc missing

quoted

+{
+	struct virtio_snd *snd = substream->snd;
+	struct virtio_snd_msg *msg;
+	unsigned int js = msecs_to_jiffies(msg_timeout_ms);
+	int rc;
+
+	msg = virtsnd_pcm_ctl_msg_alloc(substream, VIRTIO_SND_R_PCM_RELEASE,
+					GFP_KERNEL);
+	if (IS_ERR(msg))
+		return PTR_ERR(msg);
+
+	rc = virtsnd_ctl_msg_send_sync(snd, msg);
+	if (rc)
+		return rc;
+
+	return wait_event_interruptible_timeout(substream->msg_empty,
+						virtsnd_pcm_released(substream),
+						js);

wait_event_interruptible_timeout() will return a positive number in 
success cases, 0 means a timeout and condition still false. Whereas when 
you call this function you interpret 0 as success and you expect any != 0 
to be a negative error. Wondering how this worked during your tests?

Thanks
Guennadi
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