Re: [PATCH] ptr_ring: add barriers

[George Cherian]

Hi David,

On 12/11/2017 09:23 PM, David Miller wrote:
> From: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
> 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 <george.cherian@xxxxxxxxxx>
> > Suggested-by: Jason Wang <jasowang@xxxxxxxxxx>
> > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
>
> I'm asked for asking for testing feedback and did not get it in a
> reasonable amount of time.
The tests have completed more than 48 hours without any failures.
I won't interrupt the same and run for longer time.
In case of any issue I will report the same.
> So I'm applying this as-is, and queueing it up for -stable.
>
> Thank you.

Regards,
-George
>