From mboxrd@z Thu Jan 1 00:00:00 1970 From: "David J. Wilder" Subject: rnfs: rq_respages pointer is bad Date: Mon, 01 Mar 2010 16:27:00 -0800 Message-ID: <1267489621.9774.41.camel@wilder.ibm.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Tom Tucker , linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, pradeep-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org List-Id: linux-rdma@vger.kernel.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. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html