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Ting-Han Hou
f0e9db0f84
Since commitfe981e6756("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:fe981e6756("ALSA: virtio: use ack callback") Assisted-by: LLM Signed-off-by: Ting-Han Hou <ue081723@gmail.com> Link: https://patch.msgid.link/20261011125426.35745-1-ue081723@gmail.com Signed-off-by: Takashi Iwai <tiwai@suse.de>