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path: root/drivers/net/ethernet/sfc/ptp.c
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Diffstat (limited to 'drivers/net/ethernet/sfc/ptp.c')
-rw-r--r--drivers/net/ethernet/sfc/ptp.c22
1 files changed, 22 insertions, 0 deletions
diff --git a/drivers/net/ethernet/sfc/ptp.c b/drivers/net/ethernet/sfc/ptp.c
index 4625f85acab2..10ad0b93d283 100644
--- a/drivers/net/ethernet/sfc/ptp.c
+++ b/drivers/net/ethernet/sfc/ptp.c
@@ -1100,7 +1100,29 @@ static void efx_ptp_xmit_skb_queue(struct efx_nic *efx, struct sk_buff *skb)
tx_queue = efx_channel_get_tx_queue(ptp_data->channel, type);
if (tx_queue && tx_queue->timestamping) {
+ /* This code invokes normal driver TX code which is always
+ * protected from softirqs when called from generic TX code,
+ * which in turn disables preemption. Look at __dev_queue_xmit
+ * which uses rcu_read_lock_bh disabling preemption for RCU
+ * plus disabling softirqs. We do not need RCU reader
+ * protection here.
+ *
+ * Although it is theoretically safe for current PTP TX/RX code
+ * running without disabling softirqs, there are three good
+ * reasond for doing so:
+ *
+ * 1) The code invoked is mainly implemented for non-PTP
+ * packets and it is always executed with softirqs
+ * disabled.
+ * 2) This being a single PTP packet, better to not
+ * interrupt its processing by softirqs which can lead
+ * to high latencies.
+ * 3) netdev_xmit_more checks preemption is disabled and
+ * triggers a BUG_ON if not.
+ */
+ local_bh_disable();
efx_enqueue_skb(tx_queue, skb);
+ local_bh_enable();
} else {
WARN_ONCE(1, "PTP channel has no timestamped tx queue\n");
dev_kfree_skb_any(skb);