Messages in this thread Patch in this message | | | Date | Mon, 28 Jan 2013 10:42:32 -0500 | From | Konrad Rzeszutek Wilk <> | Subject | Re: [Xen-devel] [PATCH 3/3] xen/blkback: Check for insane amounts of request on the ring. |
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On Mon, Jan 28, 2013 at 11:07:46AM +0000, Jan Beulich wrote: > >>> On 25.01.13 at 19:43, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote: > > @@ -764,6 +768,9 @@ __do_block_io_op(struct xen_blkif *blkif) > > rp = blk_rings->common.sring->req_prod; > > rmb(); /* Ensure we see queued requests up to 'rp'. */ > > > > + if (RING_REQUEST_PROD_OVERFLOW(&blk_rings->common, rp, rc)) > > + return -EACCES; > > Actually I wonder whether we need the new macro at all: It seems > to me that using RING_REQUEST_CONS_OVERFLOW(&blk_rings->common, rp) > here would achieve the same effect.
But it would not. The RING_REQUEST_CONS_OVERFLOW only check that the non-shared ring entries (rsp_prod and rsp_prod_pvt) are less than the size of the ring (32). In other words - they check whether we want to process more requests as we still have a back-log of responses to deal with.
This new macro would check for the req_prod being bogus and out of bounds. Bounds being the difference between rsp_prod and req_prod being bigger than ring (32).
> > Jan > > > + > > while (rc != rp) { > > > > if (RING_REQUEST_CONS_OVERFLOW(&blk_rings->common, rc)) > >
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