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Subject[PATCH AUTOSEL 4.4 08/17] s390/qdio: add sanity checks to the fast-requeue path
Date
From: Julian Wiedmann <jwi@linux.ibm.com>

[ 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 d64b401f3d058..51cdccaec1648 100644
--- a/drivers/s390/cio/qdio_main.c
+++ b/drivers/s390/cio/qdio_main.c
@@ -1575,13 +1575,13 @@ 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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