From f0e9db0f84249b65a72b5fba43e91212281ad378 Mon Sep 17 00:00:00 2001 From: Ting-Han Hou Date: Sun, 11 Oct 2026 20:54:26 +0800 Subject: [PATCH] ALSA: virtio: reset I/O message fill level on prepare Since commit fe981e67568c ("ALSA: virtio: use ack callback"), an I/O message is only queued to the device once the application has filled the whole period: virtsnd_pcm_msg_send() accumulates the transferred bytes in msg->length and queues the message when it reaches period_bytes. msg->length is reset to 0 only when the device completes the message. If the substream is stopped (e.g. snd_pcm_drop()) while a period is only partially filled, the corresponding message is never queued and keeps its partial length. virtsnd_pcm_prepare() resets msg_count, hw_ptr and the indirect PCM state, but not msg->length. After the next start, the stale length is added to the new data, the sum never equals period_bytes, and the message is never sent again. Playback then stalls once hw_ptr reaches that period: writes fail with -EIO ("DMA or IRQ trouble") and drain fails with -EIO. Capture is affected the same way after a partial read. Clear the fill level of all messages in prepare. Outside of the resume path, virtsnd_pcm_prepare() already refuses to run while I/O messages are pending, so no message is owned by the device at this point and the reset does not race with message completion. Reproduced in QEMU (virtio-sound-pci, wav audiodev): prepare, write 1.5 periods, drop, prepare, write 16 full periods, drain. Without this patch WRITEI returns -EIO after 14 periods and DRAIN fails; with it all 16 periods are played and DRAIN succeeds. Period-aligned prefill works in both cases. The same sequence on capture (read 1.5 periods, drop, prepare, read 16 periods) fails with -EIO after 10 periods without this patch and reads all 16 with it. Found by code inspection, confirmed with the reproducer above. Fixes: fe981e67568c ("ALSA: virtio: use ack callback") Assisted-by: LLM Signed-off-by: Ting-Han Hou Link: https://patch.msgid.link/20261011125426.35745-1-ue081723@gmail.com Signed-off-by: Takashi Iwai --- sound/virtio/virtio_pcm.h | 2 ++ sound/virtio/virtio_pcm_msg.c | 19 +++++++++++++++++++ sound/virtio/virtio_pcm_ops.c | 1 + 3 files changed, 22 insertions(+) diff --git a/sound/virtio/virtio_pcm.h b/sound/virtio/virtio_pcm.h index 368dafa5df3f..8837dfc12828 100644 --- a/sound/virtio/virtio_pcm.h +++ b/sound/virtio/virtio_pcm.h @@ -118,6 +118,8 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss, void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss); +void virtsnd_pcm_msg_reset(struct virtio_pcm_substream *vss); + int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, unsigned long offset, unsigned long bytes); diff --git a/sound/virtio/virtio_pcm_msg.c b/sound/virtio/virtio_pcm_msg.c index a5c4e7027717..72103f606716 100644 --- a/sound/virtio/virtio_pcm_msg.c +++ b/sound/virtio/virtio_pcm_msg.c @@ -182,6 +182,25 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss) vss->nmsgs = 0; } +/** + * virtsnd_pcm_msg_reset() - Reset the fill level of all I/O messages. + * @vss: VirtIO PCM substream. + * + * Messages that were only partially filled by the application when the + * substream was stopped are never sent to the device, so their length must be + * cleared before the substream is started again. + * + * Context: Any context. Takes and releases the VirtIO substream spinlock. + */ +void virtsnd_pcm_msg_reset(struct virtio_pcm_substream *vss) +{ + unsigned int i; + + guard(spinlock_irqsave)(&vss->lock); + for (i = 0; vss->msgs && i < vss->nmsgs; ++i) + vss->msgs[i]->length = 0; +} + /** * virtsnd_pcm_msg_send() - Send asynchronous I/O messages. * @vss: VirtIO PCM substream. diff --git a/sound/virtio/virtio_pcm_ops.c b/sound/virtio/virtio_pcm_ops.c index 1105e7ff3523..1091100a4c98 100644 --- a/sound/virtio/virtio_pcm_ops.c +++ b/sound/virtio/virtio_pcm_ops.c @@ -299,6 +299,7 @@ static int virtsnd_pcm_prepare(struct snd_pcm_substream *substream) vss->xfer_xrun = false; vss->suspended = false; vss->msg_count = 0; + virtsnd_pcm_msg_reset(vss); memset(&vss->pcm_indirect, 0, sizeof(vss->pcm_indirect)); vss->pcm_indirect.sw_buffer_size =