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    Subject[PATCH 4.2 54/54] svcrdma: handle rdma read with a non-zero initial page offset
    Date
    4.2-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Steve Wise <swise@opengridcomputing.com>

    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.

    Fixes: 0bf4828983df ('svcrdma: refactor marshalling logic')
    Signed-off-by: Steve Wise <swise@opengridcomputing.com>
    Tested-by: Chuck Lever <chuck.lever@oracle.com>
    Signed-off-by: J. Bruce Fields <bfields@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

    --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
    +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
    @@ -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;



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