From: Greg Kroah-Hartman gregkh@linuxfoundation.org
From: Vladimir Oltean vladimir.oltean@nxp.com
commit 29d98f54a4fe1b6a9089bec8715a1b89ff9ad59c upstream.
The txtime is passed to the driver in skb->skb_mstamp_ns, which is actually in a union with skb->tstamp (the place where software timestamps are kept).
Since commit b50a5c70ffa4 ("net: allow simultaneous SW and HW transmit timestamping"), __sock_recv_timestamp has some logic for making sure that the two calls to skb_tstamp_tx:
skb_tx_timestamp(skb) # Software timestamp in the driver -> skb_tstamp_tx(skb, NULL)
and
skb_tstamp_tx(skb, &shhwtstamps) # Hardware timestamp in the driver
will both do the right thing and in a race-free manner, meaning that skb_tx_timestamp will deliver a cmsg with the software timestamp only, and skb_tstamp_tx with a non-NULL hwtstamps argument will deliver a cmsg with the hardware timestamp only.
Why are races even possible? Well, because although the software timestamp skb->tstamp is private per skb, the hardware timestamp skb_hwtstamps(skb) lives in skb_shinfo(skb), an area which is shared between skbs and their clones. And skb_tstamp_tx works by cloning the packets when timestamping them, therefore attempting to perform hardware timestamping on an skb's clone will also change the hardware timestamp of the original skb. And the original skb might have been yet again cloned for software timestamping, at an earlier stage.
So the logic in __sock_recv_timestamp can't be as simple as saying "does this skb have a hardware timestamp? if yes I'll send the hardware timestamp to the socket, otherwise I'll send the software timestamp", precisely because the hardware timestamp is shared. Instead, it's quite the other way around: __sock_recv_timestamp says "does this skb have a software timestamp? if yes, I'll send the software timestamp, otherwise the hardware one". This works because the software timestamp is not shared with clones.
But that means we have a problem when we attempt hardware timestamping with skbs that don't have the skb->tstamp == 0. __sock_recv_timestamp will say "oh, yeah, this must be some sort of odd clone" and will not deliver the hardware timestamp to the socket. And this is exactly what is happening when we have txtime enabled on the socket: as mentioned, that is put in a union with skb->tstamp, so it is quite easy to mistake it.
Do what other drivers do (intel igb/igc) and write zero to skb->tstamp before taking the hardware timestamp. It's of no use to us now (we're already on the TX confirmation path).
Fixes: 0d08c9ec7d6e ("enetc: add support time specific departure base on the qos etf") Cc: Vinicius Costa Gomes vinicius.gomes@intel.com Signed-off-by: Vladimir Oltean vladimir.oltean@nxp.com Acked-by: Vinicius Costa Gomes vinicius.gomes@intel.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/ethernet/freescale/enetc/enetc.c | 6 ++++++ 1 file changed, 6 insertions(+)
--- a/drivers/net/ethernet/freescale/enetc/enetc.c +++ b/drivers/net/ethernet/freescale/enetc/enetc.c @@ -344,6 +344,12 @@ static void enetc_tstamp_tx(struct sk_bu if (skb_shinfo(skb)->tx_flags & SKBTX_IN_PROGRESS) { memset(&shhwtstamps, 0, sizeof(shhwtstamps)); shhwtstamps.hwtstamp = ns_to_ktime(tstamp); + /* Ensure skb_mstamp_ns, which might have been populated with + * the txtime, is not mistaken for a software timestamp, + * because this will prevent the dispatch of our hardware + * timestamp to the socket. + */ + skb->tstamp = ktime_set(0, 0); skb_tstamp_tx(skb, &shhwtstamps); } }