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ALSA: xen-front: Reset event channel state on stream clear

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xen_snd_front_evtchnl_pair_clear() resets evt_next_id for both
channels. That is correct for the request channel, where evt_next_id is
used to allocate the next request id. It is wrong for the event channel:
incoming events are validated against evt_id, and evt_id is incremented
by evtchnl_interrupt_evt().

This leaves the expected event id from the previous stream instance. A
backend that restarts event ids for a reopened stream can then have valid
current-position events dropped until the stale frontend id catches up.

Reset evt_id for the event channel. Also advance the event-page consumer
to the current producer while clearing the stream, so obsolete events
queued for the previous stream instance are not delivered to the next
ALSA runtime.

Fixes: 1cee559351 ("ALSA: xen-front: Implement ALSA virtual sound driver")
Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>
Link: https://patch.msgid.link/20260526-alsa-xen-event-channel-fixes-v1-1-91d3a6a50778@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Cássio Gabriel 2026-05-26 09:48:26 -03:00 committed by Takashi Iwai
parent a238120042
commit 9cd8115237
2 changed files with 8 additions and 4 deletions
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8
sound/xen/xen_snd_front_evtchnl.c
View File

@ -456,7 +456,11 @@ void xen_snd_front_evtchnl_pair_clear(struct xen_snd_front_evtchnl_pair *evt_pai
}
scoped_guard(mutex, &evt_pair->evt.ring_io_lock) {
evt_pair->evt.evt_next_id = 0;
evt_pair->evt.evt_id = 0;
/* Drop obsolete events queued for the previous stream instance. */
evt_pair->evt.u.evt.page->in_cons =
evt_pair->evt.u.evt.page->in_prod;
/* Ensure the consumer index is visible before stream reuse. */
virt_wmb();
}
}

4
sound/xen/xen_snd_front_evtchnl.h
View File

@ -37,9 +37,9 @@ struct xen_snd_front_evtchnl {
/* State of the event channel. */
enum xen_snd_front_evtchnl_state state;
enum xen_snd_front_evtchnl_type type;
/* Either response id or incoming event id. */
/* Current response id or next expected incoming event id. */
u16 evt_id;
/* Next request id or next expected event id. */
/* Next request id. */
u16 evt_next_id;
/* Shared ring access lock. */
struct mutex ring_io_lock;