ptr_ring: add barriers
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: NGeorge Cherian <george.cherian@cavium.com> Suggested-by: NJason Wang <jasowang@redhat.com> Signed-off-by: NMichael S. Tsirkin <mst@redhat.com> Acked-by: NJason Wang <jasowang@redhat.com> Signed-off-by: NDavid S. Miller <davem@davemloft.net>
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