s390/qeth: fix race in used-buffer accounting

[ 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/s390/net/qeth_core_main.c b/drivers/s390/net/qeth_core_main.c
index 283416aefa564af20cfb0b9987302a080e0b308e..258a72869f57597bfad14309c8bd6b45755b4795 100644 (file)
--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -3499,13 +3499,14 @@ static void qeth_flush_buffers(struct qeth_qdio_out_q *queue, int index,
        qdio_flags = QDIO_FLAG_SYNC_OUTPUT;
        if (atomic_read(&queue->set_pci_flags_count))
                qdio_flags |= QDIO_FLAG_PCI_OUT;
+       atomic_add(count, &queue->used_buffers);
+
        rc = 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 +=
                        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 += count;
                /* ignore temporary SIGA errors without busy condition */