FAILED: patch "[PATCH] svcrdma: handle rdma read with a non-zero initial page offset" failed to apply to 4.2-stable tree

The patch below does not apply to the 4.2-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

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

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.

index cb5174284074..5f6ca47092b0 100644
@@ -136,7 +136,8 @@ int rdma_read_chunk_lcl(struct svcxprt_rdma *xprt,
 	ctxt->direction = DMA_FROM_DEVICE;
 	ctxt->read_hdr = head;
 	pages_needed = min_t(int, pages_needed, xprt->sc_max_sge_rd);
-	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);

@@ -235,7 +236,8 @@ int rdma_read_chunk_frmr(struct svcxprt_rdma *xprt,
 	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;