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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Julian Wiedmann <jwi@linux.ibm.com>,
        "David S . Miller" <davem@davemloft.net>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL 4.18 73/88] s390/qeth: fix race in used-buffer
 accounting
Thread-Topic: [PATCH AUTOSEL 4.18 73/88] s390/qeth: fix race in used-buffer
 accounting
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Date:   Fri, 7 Sep 2018 00:36:43 +0000
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From: Julian Wiedmann <jwi@linux.ibm.com>

[ Upstream commit a702349a4099cd5a7bab0904689d8e0bf8dcd622 ]

By updating q->used_buffers only _after_ do_QDIO() has completed, there
is a potential race against the buffer's TX completion. In the unlikely
case that the TX completion path wins, qeth_qdio_output_handler() would
decrement the counter before qeth_flush_buffers() even incremented it.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 drivers/s390/net/qeth_core_main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/s390/net/qeth_core_main.c b/drivers/s390/net/qeth_core=
_main.c
index d01ac29fd986..ffdb78421a25 100644
--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -3530,13 +3530,14 @@ static void qeth_flush_buffers(struct qeth_qdio_out=
_q *queue, int index,
 	qdio_flags =3D QDIO_FLAG_SYNC_OUTPUT;
 	if (atomic_read(&queue->set_pci_flags_count))
 		qdio_flags |=3D QDIO_FLAG_PCI_OUT;
+	atomic_add(count, &queue->used_buffers);
+
 	rc =3D do_QDIO(CARD_DDEV(queue->card), qdio_flags,
 		     queue->queue_no, index, count);
 	if (queue->card->options.performance_stats)
 		queue->card->perf_stats.outbound_do_qdio_time +=3D
 			qeth_get_micros() -
 			queue->card->perf_stats.outbound_do_qdio_start_time;
-	atomic_add(count, &queue->used_buffers);
 	if (rc) {
 		queue->card->stats.tx_errors +=3D count;
 		/* ignore temporary SIGA errors without busy condition */
--=20
2.17.1