Re: [Xen-devel] barriers before {req/rsp}_cons = cons?

[Samuel Thibault <samuel.thibault@xxxxxxxxxxxxx>]

Keir Fraser, le Fri 18 Jul 2008 20:31:13 +0100, a écrit :
> > cons = netif->tx.req_cons;
> > rmb(); /* Ensure that we see the request before we copy it. */
> > memcpy(&txreq, RING_GET_REQUEST(&netif->tx, i), sizeof(txreq));
> > some checks
> > netif->tx.req_cons = ++cons;
> 
> Could you describe the race you believe is made possible by the absence of
> the barrier?

It is very unlikely, but the write into req_cons could happen before
actually doing the memcpy, and so another processor could try to reuse
the same request slot.

Samuel

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