From: Tom Tucker Date: Wed, 26 Mar 2008 02:27:19 +0000 (-0400) Subject: SVCRDMA: Check num_sge when setting LAST_CTXT bit X-Git-Tag: v2.6.25-rc8~86 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c8237a5fcea9d49a73275b4c8f541dd42f8da1a4;p=linux-2.6 SVCRDMA: Check num_sge when setting LAST_CTXT bit The RDMACTXT_F_LAST_CTXT bit was getting set incorrectly when the last chunk in the read-list spanned multiple pages. This resulted in a kernel panic when the wrong context was used to build the RPC iovec page list. RDMA_READ is used to fetch RPC data from the client for NFS_WRITE requests. A scatter-gather is used to map the advertised client side buffer to the server-side iovec and associated page list. WR contexts are used to convey which scatter-gather entries are handled by each WR. When the write data is large, a single RPC may require multiple RDMA_READ requests so the contexts for a single RPC are chained together in a linked list. The last context in this list is marked with a bit RDMACTXT_F_LAST_CTXT so that when this WR completes, the CQ handler code can enqueue the RPC for processing. The code in rdma_read_xdr was setting this bit on the last two contexts on this list when the last read-list chunk spanned multiple pages. This caused the svc_rdma_recvfrom logic to incorrectly build the RPC and caused the kernel to crash because the second-to-last context doesn't contain the iovec page list. Modified the condition that sets this bit so that it correctly detects the last context for the RPC. Signed-off-by: Tom Tucker Tested-by: Roland Dreier Signed-off-by: J. Bruce Fields Signed-off-by: Linus Torvalds --- diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c index 971271602d..c22d6b6f2d 100644 --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c @@ -322,15 +322,6 @@ next_sge: ctxt->direction = DMA_FROM_DEVICE; clear_bit(RDMACTXT_F_READ_DONE, &ctxt->flags); clear_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags); - if ((ch+1)->rc_discrim == 0) { - /* - * Checked in sq_cq_reap to see if we need to - * be enqueued - */ - set_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags); - ctxt->next = hdr_ctxt; - hdr_ctxt->next = head; - } /* Prepare READ WR */ memset(&read_wr, 0, sizeof read_wr); @@ -348,7 +339,17 @@ next_sge: rdma_set_ctxt_sge(ctxt, &sge[ch_sge_ary[ch_no].start], &sgl_offset, read_wr.num_sge); - + if (((ch+1)->rc_discrim == 0) && + (read_wr.num_sge == ch_sge_ary[ch_no].count)) { + /* + * Mark the last RDMA_READ with a bit to + * indicate all RPC data has been fetched from + * the client and the RPC needs to be enqueued. + */ + set_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags); + ctxt->next = hdr_ctxt; + hdr_ctxt->next = head; + } /* Post the read */ err = svc_rdma_send(xprt, &read_wr); if (err) {