D46155.diff
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	diff --git a/sys/sys/buf_ring.h b/sys/sys/buf_ring.h
	--- a/sys/sys/buf_ring.h
	+++ b/sys/sys/buf_ring.h
	@@ -89,7 +89,17 @@
	#endif
	critical_enter();
	do {
	- prod_head = br->br_prod_head;
	+ /*
	+ * br->br_prod_head needs to be read before br->br_cons_tail.
	+ * If not then we could perform the dequeue and enqueue
	+ * between reading br_cons_tail and reading br_prod_head. This
	+ * could give us values where br_cons_head == br_prod_tail
	+ * (after masking).
	+ *
	+ * To work around this us a load acquire. This is just to
	+ * ensure ordering within this thread.
	+ */
	+ prod_head = atomic_load_acq_32(&br->br_prod_head);
	prod_next = prod_head + 1;
	cons_tail = atomic_load_acq_32(&br->br_cons_tail);

	@@ -137,7 +147,12 @@
	critical_enter();
	mask = br->br_cons_mask;
	do {
	- cons_head = br->br_cons_head;
	+ /*
	+ * As with buf_ring_enqueue ensure we read the head before
	+ * the tail. If we read them in the wrong order we may
	+ * think the bug_ring is full when it is empty.
	+ */
	+ cons_head = atomic_load_acq_32(&br->br_cons_head);
	cons_next = cons_head + 1;
	prod_tail = atomic_load_acq_32(&br->br_prod_tail);