D19932.id56325.diff
No OneTemporary
Actions

Size

1 KB

Referenced Files

None

Subscribers

None

D19932.id56325.diff
View Options

	Index: sys/sys/buf_ring.h
	===================================================================
	--- sys/sys/buf_ring.h
	+++ sys/sys/buf_ring.h
	@@ -310,15 +310,24 @@
	if (!mtx_owned(br->br_lock))
	panic("lock not held on single consumer dequeue");
	#endif
	- /*
	- * I believe it is safe to not have a memory barrier
	- * here because we control cons and tail is worst case
	- * a lagging indicator so we worst case we might
	- * return NULL immediately after a buffer has been enqueued
	- */
	+
	if (br->br_cons_head == br->br_prod_tail)
	return (NULL);

	+#if defined(__arm__) \|\| defined(__aarch64__)
	+ /*
	+ * The barrier is required there on ARM and ARM64 to ensure, that
	+ * br->br_ring[br->br_cons_head] will not be fetched before the above
	+ * condition is checked.
	+ * Without the barrier, it is possible, that buffer will be fetched
	+ * before the enqueue will put mbuf into br, then, in the meantime, the
	+ * enqueue will update the array and the br_prod_tail, and the
	+ * conditional check will be true, so we will return previously fetched
	+ * (and invalid) buffer.
	+ */
	+ atomic_thread_fence_acq();
	+#endif
	+
	#ifdef DEBUG_BUFRING
	/*
	* Single consumer, i.e. cons_head will not move while we are