rnfs: rq_respages pointer is bad

David J. Wilder
2010-03-02T00:27:00Z

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.