linux-kernel - [PATCH 3.10 154/250] s390/qdio: clear DSCI prior to scanning multiple input queues

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Date:   Thu,  8 Jun 2017 00:59:00 +0200
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Julian Wiedmann <jwi@...ux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 154/250] s390/qdio: clear DSCI prior to scanning multiple input queues

From: Julian Wiedmann <jwi@...ux.vnet.ibm.com>

commit 1e4a382fdc0ba8d1a85b758c0811de3a3631085e upstream.

For devices with multiple input queues, tiqdio_call_inq_handlers()
iterates over all input queues and clears the device's DSCI
during each iteration. If the DSCI is re-armed during one
of the later iterations, we therefore do not scan the previous
queues again.
The re-arming also raises a new adapter interrupt. But its
handler does not trigger a rescan for the device, as the DSCI
has already been erroneously cleared.
This can result in queue stalls on devices with multiple
input queues.

Fix it by clearing the DSCI just once, prior to scanning the queues.

As the code is moved in front of the loop, we also need to access
the DSCI directly (ie irq->dsci) instead of going via each queue's
parent pointer to the same irq. This is not a functional change,
and a follow-up patch will clean up the other users.

In practice, this bug only affects CQ-enabled HiperSockets devices,
ie. devices with sysfs-attribute "hsuid" set. Setting a hsuid is
needed for AF_IUCV socket applications that use HiperSockets
communication.

Fixes: 104ea556ee7f ("qdio: support asynchronous delivery of storage blocks")
Reviewed-by: Ursula Braun <ubraun@...ux.vnet.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@...ux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
Signed-off-by: Willy Tarreau <w@....eu>
---
 drivers/s390/cio/qdio_thinint.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/s390/cio/qdio_thinint.c b/drivers/s390/cio/qdio_thinint.c
index bde5255..1d1e585 100644
--- a/drivers/s390/cio/qdio_thinint.c
+++ b/drivers/s390/cio/qdio_thinint.c
@@ -142,11 +142,11 @@ static inline void tiqdio_call_inq_handlers(struct qdio_irq *irq)
 	struct qdio_q *q;
 	int i;

-	for_each_input_queue(irq, q, i) {
-		if (!references_shared_dsci(irq) &&
-		    has_multiple_inq_on_dsci(irq))
-			xchg(q->irq_ptr->dsci, 0);
+	if (!references_shared_dsci(irq) &&
+	    has_multiple_inq_on_dsci(irq))
+		xchg(irq->dsci, 0);

+	for_each_input_queue(irq, q, i) {
 		if (q->u.in.queue_start_poll) {
 			/* skip if polling is enabled or already in work */
 			if (test_and_set_bit(QDIO_QUEUE_IRQS_DISABLED,
-- 
2.8.0.rc2.1.gbe9624a