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

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: 1cee559351a7 ("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>

diff --git a/sound/xen/xen_snd_front_evtchnl.c b/sound/xen/xen_snd_front_evtchnl.c
index bc03f71bf16e3372832c096e1f0cee09c14cff18..09e4c1d0563632b6d8b846932949872cb126f37f 100644 (file)
--- a/sound/xen/xen_snd_front_evtchnl.c
+++ b/sound/xen/xen_snd_front_evtchnl.c
@@ -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();
        }
 }
-

diff --git a/sound/xen/xen_snd_front_evtchnl.h b/sound/xen/xen_snd_front_evtchnl.h
index 3675fba705647dcf7f9732136ca072fee115b682..8400261ac4660139e047bb2a789456a3f1b46a8c 100644 (file)
--- a/sound/xen/xen_snd_front_evtchnl.h
+++ b/sound/xen/xen_snd_front_evtchnl.h
@@ -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;