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    Subject[PATCH 4.4 14/78] s390/qdio: add sanity checks to the fast-requeue path
    Date
    [ Upstream commit a6ec414a4dd529eeac5c3ea51c661daba3397108 ]

    If the device driver were to send out a full queue's worth of SBALs,
    current code would end up discovering the last of those SBALs as PRIMED
    and erroneously skip the SIGA-w. This immediately stalls the queue.

    Add a check to not attempt fast-requeue in this case. While at it also
    make sure that the state of the previous SBAL was successfully extracted
    before inspecting it.

    Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
    Reviewed-by: Jens Remus <jremus@linux.ibm.com>
    Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/s390/cio/qdio_main.c | 12 ++++++------
    1 file changed, 6 insertions(+), 6 deletions(-)

    diff --git a/drivers/s390/cio/qdio_main.c b/drivers/s390/cio/qdio_main.c
    index 8d7fc3b6ca63f..adf322a86a01b 100644
    --- a/drivers/s390/cio/qdio_main.c
    +++ b/drivers/s390/cio/qdio_main.c
    @@ -1576,13 +1576,13 @@ static int handle_outbound(struct qdio_q *q, unsigned int callflags,
    rc = qdio_kick_outbound_q(q, phys_aob);
    } else if (need_siga_sync(q)) {
    rc = qdio_siga_sync_q(q);
    + } else if (count < QDIO_MAX_BUFFERS_PER_Q &&
    + get_buf_state(q, prev_buf(bufnr), &state, 0) > 0 &&
    + state == SLSB_CU_OUTPUT_PRIMED) {
    + /* The previous buffer is not processed yet, tack on. */
    + qperf_inc(q, fast_requeue);
    } else {
    - /* try to fast requeue buffers */
    - get_buf_state(q, prev_buf(bufnr), &state, 0);
    - if (state != SLSB_CU_OUTPUT_PRIMED)
    - rc = qdio_kick_outbound_q(q, 0);
    - else
    - qperf_inc(q, fast_requeue);
    + rc = qdio_kick_outbound_q(q, 0);
    }

    /* in case of SIGA errors we must process the error immediately */
    --
    2.20.1


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