Re: [PATCH] ptr_ring: add barriers

From: "Michael S. Tsirkin" <mst@redhat.com>
Date: Tue, 5 Dec 2017 21:29:37 +0200

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 <redacted>
Suggested-by: Jason Wang <redacted>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

I'm asked for asking for testing feedback and did not get it in a
reasonable amount of time.

So I'm applying this as-is, and queueing it up for -stable.

Thank you.