D57399.diff
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	diff --git a/sys/dev/sound/pcm/dsp.c b/sys/dev/sound/pcm/dsp.c
	--- a/sys/dev/sound/pcm/dsp.c
	+++ b/sys/dev/sound/pcm/dsp.c
	@@ -2742,16 +2742,29 @@

	/* Proceed only if no errors encountered. */
	if (ret == 0) {
	- /* Launch channels */
	- while ((sm = SLIST_FIRST(&sg->members)) != NULL) {
	- SLIST_REMOVE_HEAD(&sg->members, link);
	+ /*
	+ * Unlock all members before starting any of them.
	+ * Holding multiple channel locks while calling chn_start()
	+ * on a virtual channel can trigger the parent, which
	+ * acquires PCM_LOCK() while other virtual channels are
	+ * still locked -- a lock order reversal.
	+ */
	+ SLIST_FOREACH(sm, &sg->members, link) {
	+ sm->ch->sm = NULL;
	+ sm->ch->flags &= ~CHN_F_NOTRIGGER;
	+ CHN_UNLOCK(sm->ch);
	+ }

	+ /*
	+ * Start each channel individually, then remove it from
	+ * the sync group and free its member structure.
	+ */
	+ while ((sm = SLIST_FIRST(&sg->members)) != NULL) {
	c = sm->ch;
	- c->sm = NULL;
	+ CHN_LOCK(c);
	chn_start(c, 1);
	- c->flags &= ~CHN_F_NOTRIGGER;
	CHN_UNLOCK(c);
	-
	+ SLIST_REMOVE_HEAD(&sg->members, link);
	free(sm, M_DEVBUF);
	}