Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net

No conflicts.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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);