rnfs: rq_respages pointer is bad

["David J. Wilder" <dwilder-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Tom

I have been chasing an rnfs related Oops in svc_process().  I have found
the source of the Oops but I am not sure of my fix.  I am seeing the
problem on ppc64, kernel 2.6.32, I have not tried other arch yet.

The source of the problem is in rdma_read_complete(), I am finding that
rqstp->rq_respages is set to point past the end of the rqstp->rq_pages
page list.  This results in a NULL reference in svc_process() when
passing rq_respages[0] to page_address().

In rdma_read_complete() we are using rqstp->rq_arg.pages as the base of
the page list then indexing by page_no, however rq_arg.pages is not
pointing to the start of the list so rq_respages ends up pointing to:

rqstp->rq_pages[(head->count+1) + head->hdr_count]

In my case, it ends up pointing one past the end of the list by one.

Here is the change I made.

static int rdma_read_complete(struct svc_rqst *rqstp,
                              struct svc_rdma_op_ctxt *head)
{
        int page_no;
        int ret;

        BUG_ON(!head);

        /* Copy RPC pages */
        for (page_no = 0; page_no < head->count; page_no++) {
                put_page(rqstp->rq_pages[page_no]);
                rqstp->rq_pages[page_no] = head->pages[page_no];
        }
        /* Point rq_arg.pages past header */
        rqstp->rq_arg.pages = &rqstp->rq_pages[head->hdr_count];
        rqstp->rq_arg.page_len = head->arg.page_len;
        rqstp->rq_arg.page_base = head->arg.page_base;

        /* rq_respages starts after the last arg page */
-       rqstp->rq_respages = &rqstp->rq_arg.pages[page_no];
+	rqstp->rq_respages = &rqstp->rq_pages[page_no];
.
.
.

The change works for me, but I am not sure it is safe to assume the
rqstp->rq_pages[head->count] will always point to the last arg page.

Dave.

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