Patch "svcrdma: handle rdma read with a non-zero initial page offset" has been added to the 4.1-stable tree

This is a note to let you know that I've just added the patch titled

svcrdma: handle rdma read with a non-zero initial page offset

to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
svcrdma-handle-rdma-read-with-a-non-zero-initial-page-offset.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Steve Wise <[email protected]>
Date: Mon, 28 Sep 2015 16:46:06 -0500
Subject: svcrdma: handle rdma read with a non-zero initial page offset

From: Steve Wise <[email protected]>

commit c91aed9896946721bb30705ea2904edb3725dd61 upstream.

The server rdma_read_chunk_lcl() and rdma_read_chunk_frmr() functions were not taking into account the initial page_offset when determining the rdma read length. This resulted in a read who's starting address and length exceeded the base/bounds of the frmr.

The server gets an async error from the rdma device and kills the connection, and the client then reconnects and resends. This repeats indefinitely, and the application hangs.

Most work loads don't tickle this bug apparently, but one test hit it every time: building the linux kernel on a 16 core node with 'make -j 16 O=/mnt/0' where /mnt/0 is a ramdisk mounted via NFSRDMA.

This bug seems to only be tripped with devices having small fastreg page list depths. I didn't see it with mlx4, for instance.

---
 net/sunrpc/xprtrdma/svc_rdma_recvfrom.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

@@ -146,7 +146,8 @@ int rdma_read_chunk_lcl(struct svcxprt_r
 	ctxt->read_hdr = head;
 	pages_needed =
 		min_t(int, pages_needed, rdma_read_max_sge(xprt, pages_needed));
-	read = min_t(int, pages_needed << PAGE_SHIFT, rs_length);
+	read = min_t(int, (pages_needed << PAGE_SHIFT) - *page_offset,
+		     rs_length);
 
 	for (pno = 0; pno < pages_needed; pno++) {
 		int len = min_t(int, rs_length, PAGE_SIZE - pg_off);

@@ -245,7 +246,8 @@ int rdma_read_chunk_frmr(struct svcxprt_
 	ctxt->direction = DMA_FROM_DEVICE;
 	ctxt->frmr = frmr;
 	pages_needed = min_t(int, pages_needed, xprt->sc_frmr_pg_list_len);
-	read = min_t(int, pages_needed << PAGE_SHIFT, rs_length);
+	read = min_t(int, (pages_needed << PAGE_SHIFT) - *page_offset,
+		     rs_length);
 
 	frmr->kva = page_address(rqstp->rq_arg.pages[pg_no]);
 	frmr->direction = DMA_FROM_DEVICE;

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/svcrdma-handle-rdma-read-with-a-non-zero-initial-page-offset.patch