[PATCH net-next 01/11] s390/qeth: fix race in used-buffer accounting

Julian Wiedmann
2018-07-19T10:43:48Z

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>
---
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 d80972b9bfc7..f7ddd6455638 100644
--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -3506,13 +3506,14 @@ 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 */
--
2.16.4