ptr_ring: add barriers (a8ceb5db) · Commits · 戴 / test

Users of ptr_ring expect that it's safe to give the data structure a pointer and have it be available to consumers, but that actually requires an smb_wmb or a stronger barrier. In absence of such barriers and on architectures that reorder writes, consumer might read an un=initialized value from an skb pointer stored in the skb array. This was observed causing crashes. To fix, add memory barriers. The barrier we use is a wmb, the assumption being that producers do not need to read the value so we do not need to order these reads. Reported-by:

George Cherian <george.cherian@cavium.com> Suggested-by:

Jason Wang <jasowang@redhat.com> Signed-off-by:

Michael S. Tsirkin <mst@redhat.com> Acked-by:

Jason Wang <jasowang@redhat.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

include/linux/ptr_ring.h

+9 −0

Original line number	Diff line number	Diff line
		@@ -101,12 +101,18 @@ static inline bool ptr_ring_full_bh(struct ptr_ring *r)

		/* Note: callers invoking this in a loop must use a compiler barrier,
		* for example cpu_relax(). Callers must hold producer_lock.
		* Callers are responsible for making sure pointer that is being queued
		* points to a valid data.
		*/
		static inline int __ptr_ring_produce(struct ptr_ring r, void ptr)
		{
		if (unlikely(!r->size) \|\| r->queue[r->producer])
		return -ENOSPC;

		/* Make sure the pointer we are storing points to a valid data. */
		/* Pairs with smp_read_barrier_depends in __ptr_ring_consume. */
		smp_wmb();

		r->queue[r->producer++] = ptr;
		if (unlikely(r->producer >= r->size))
		r->producer = 0;
		@@ -275,6 +281,9 @@ static inline void __ptr_ring_consume(struct ptr_ring r)
		if (ptr)
		__ptr_ring_discard_one(r);

		/* Make sure anyone accessing data through the pointer is up to date. */
		/* Pairs with smp_wmb in __ptr_ring_produce. */
		smp_read_barrier_depends();
		return ptr;
		}

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