s390/qdio: add sanity checks to the fast-requeue path

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>

diff --git a/drivers/s390/cio/qdio_main.c b/drivers/s390/cio/qdio_main.c
index 730c4e6..7f5adf0 100644 (file)
--- a/drivers/s390/cio/qdio_main.c
+++ b/drivers/s390/cio/qdio_main.c
@@ -1558,13 +1558,13 @@ 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 */