From 8a8a9fac9efa6423fd74938b940cb7d731780718 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 20 Feb 2026 22:26:05 +0000 Subject: net: do not pass flow_id to set_rps_cpu() Blamed commit made the assumption that the RPS table for each receive queue would have the same size, and that it would not change. Compute flow_id in set_rps_cpu(), do not assume we can use the value computed by get_rps_cpu(). Otherwise we risk out-of-bound access and/or crashes. Fixes: 48aa30443e52 ("net: Cache hash and flow_id to avoid recalculation") Signed-off-by: Eric Dumazet Cc: Krishna Kumar Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20260220222605.3468081-1-edumazet@google.com Signed-off-by: Jakub Kicinski --- net/core/dev.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) (limited to 'net/core/dev.c') diff --git a/net/core/dev.c b/net/core/dev.c index 096b3ff13f6b..f3426385f1ba 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -4992,8 +4992,7 @@ static bool rps_flow_is_active(struct rps_dev_flow *rflow, static struct rps_dev_flow * set_rps_cpu(struct net_device *dev, struct sk_buff *skb, - struct rps_dev_flow *rflow, u16 next_cpu, u32 hash, - u32 flow_id) + struct rps_dev_flow *rflow, u16 next_cpu, u32 hash) { if (next_cpu < nr_cpu_ids) { u32 head; @@ -5004,6 +5003,7 @@ set_rps_cpu(struct net_device *dev, struct sk_buff *skb, struct rps_dev_flow *tmp_rflow; unsigned int tmp_cpu; u16 rxq_index; + u32 flow_id; int rc; /* Should we steer this flow to a different hardware queue? */ @@ -5019,6 +5019,7 @@ set_rps_cpu(struct net_device *dev, struct sk_buff *skb, if (!flow_table) goto out; + flow_id = rfs_slot(hash, flow_table); tmp_rflow = &flow_table->flows[flow_id]; tmp_cpu = READ_ONCE(tmp_rflow->cpu); @@ -5066,7 +5067,6 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb, struct rps_dev_flow_table *flow_table; struct rps_map *map; int cpu = -1; - u32 flow_id; u32 tcpu; u32 hash; @@ -5113,8 +5113,7 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb, /* OK, now we know there is a match, * we can look at the local (per receive queue) flow table */ - flow_id = rfs_slot(hash, flow_table); - rflow = &flow_table->flows[flow_id]; + rflow = &flow_table->flows[rfs_slot(hash, flow_table)]; tcpu = rflow->cpu; /* @@ -5133,8 +5132,7 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb, ((int)(READ_ONCE(per_cpu(softnet_data, tcpu).input_queue_head) - rflow->last_qtail)) >= 0)) { tcpu = next_cpu; - rflow = set_rps_cpu(dev, skb, rflow, next_cpu, hash, - flow_id); + rflow = set_rps_cpu(dev, skb, rflow, next_cpu, hash); } if (tcpu < nr_cpu_ids && cpu_online(tcpu)) { -- cgit v1.2.3 From 7aa767d0d3d04e50ae94e770db7db8197f666970 Mon Sep 17 00:00:00 2001 From: Jakub Kicinski Date: Mon, 23 Feb 2026 15:51:00 -0800 Subject: net: consume xmit errors of GSO frames udpgro_frglist.sh and udpgro_bench.sh are the flakiest tests currently in NIPA. They fail in the same exact way, TCP GRO test stalls occasionally and the test gets killed after 10min. These tests use veth to simulate GRO. They attach a trivial ("return XDP_PASS;") XDP program to the veth to force TSO off and NAPI on. Digging into the failure mode we can see that the connection is completely stuck after a burst of drops. The sender's snd_nxt is at sequence number N [1], but the receiver claims to have received (rcv_nxt) up to N + 3 * MSS [2]. Last piece of the puzzle is that senders rtx queue is not empty (let's say the block in the rtx queue is at sequence number N - 4 * MSS [3]). In this state, sender sends a retransmission from the rtx queue with a single segment, and sequence numbers N-4*MSS:N-3*MSS [3]. Receiver sees it and responds with an ACK all the way up to N + 3 * MSS [2]. But sender will reject this ack as TCP_ACK_UNSENT_DATA because it has no recollection of ever sending data that far out [1]. And we are stuck. The root cause is the mess of the xmit return codes. veth returns an error when it can't xmit a frame. We end up with a loss event like this: ------------------------------------------------- | GSO super frame 1 | GSO super frame 2 | |-----------------------------------------------| | seg | seg | seg | seg | seg | seg | seg | seg | | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | ------------------------------------------------- x ok ok | ok ok ok \\ snd_nxt "x" means packet lost by veth, and "ok" means it went thru. Since veth has TSO disabled in this test it sees individual segments. Segment 1 is on the retransmit queue and will be resent. So why did the sender not advance snd_nxt even tho it clearly did send up to seg 8? tcp_write_xmit() interprets the return code from the core to mean that data has not been sent at all. Since TCP deals with GSO super frames, not individual segment the crux of the problem is that loss of a single segment can be interpreted as loss of all. TCP only sees the last return code for the last segment of the GSO frame (in <> brackets in the diagram above). Of course for the problem to occur we need a setup or a device without a Qdisc. Otherwise Qdisc layer disconnects the protocol layer from the device errors completely. We have multiple ways to fix this. 1) make veth not return an error when it lost a packet. While this is what I think we did in the past, the issue keeps reappearing and it's annoying to debug. The game of whack a mole is not great. 2) fix the damn return codes We only talk about NETDEV_TX_OK and NETDEV_TX_BUSY in the documentation, so maybe we should make the return code from ndo_start_xmit() a boolean. I like that the most, but perhaps some ancient, not-really-networking protocol would suffer. 3) make TCP ignore the errors It is not entirely clear to me what benefit TCP gets from interpreting the result of ip_queue_xmit()? Specifically once the connection is established and we're pushing data - packet loss is just packet loss? 4) this fix Ignore the rc in the Qdisc-less+GSO case, since it's unreliable. We already always return OK in the TCQ_F_CAN_BYPASS case. In the Qdisc-less case let's be a bit more conservative and only mask the GSO errors. This path is taken by non-IP-"networks" like CAN, MCTP etc, so we could regress some ancient thing. This is the simplest, but also maybe the hackiest fix? Similar fix has been proposed by Eric in the past but never committed because original reporter was working with an OOT driver and wasn't providing feedback (see Link). Link: https://lore.kernel.org/CANn89iJcLepEin7EtBETrZ36bjoD9LrR=k4cfwWh046GB+4f9A@mail.gmail.com Fixes: 1f59533f9ca5 ("qdisc: validate frames going through the direct_xmit path") Signed-off-by: Jakub Kicinski Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260223235100.108939-1-kuba@kernel.org Signed-off-by: Paolo Abeni --- net/core/dev.c | 23 ++++++++++++++++++----- 1 file changed, 18 insertions(+), 5 deletions(-) (limited to 'net/core/dev.c') diff --git a/net/core/dev.c b/net/core/dev.c index f3426385f1ba..3d2d3b18915c 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -4822,6 +4822,8 @@ int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev) * to -1 or to their cpu id, but not to our id. */ if (READ_ONCE(txq->xmit_lock_owner) != cpu) { + bool is_list = false; + if (dev_xmit_recursion()) goto recursion_alert; @@ -4832,17 +4834,28 @@ int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev) HARD_TX_LOCK(dev, txq, cpu); if (!netif_xmit_stopped(txq)) { + is_list = !!skb->next; + dev_xmit_recursion_inc(); skb = dev_hard_start_xmit(skb, dev, txq, &rc); dev_xmit_recursion_dec(); - if (dev_xmit_complete(rc)) { - HARD_TX_UNLOCK(dev, txq); - goto out; - } + + /* GSO segments a single SKB into + * a list of frames. TCP expects error + * to mean none of the data was sent. + */ + if (is_list) + rc = NETDEV_TX_OK; } HARD_TX_UNLOCK(dev, txq); + if (!skb) /* xmit completed */ + goto out; + net_crit_ratelimited("Virtual device %s asks to queue packet!\n", dev->name); + /* NETDEV_TX_BUSY or queue was stopped */ + if (!is_list) + rc = -ENETDOWN; } else { /* Recursion is detected! It is possible, * unfortunately @@ -4850,10 +4863,10 @@ int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev) recursion_alert: net_crit_ratelimited("Dead loop on virtual device %s, fix it urgently!\n", dev->name); + rc = -ENETDOWN; } } - rc = -ENETDOWN; rcu_read_unlock_bh(); dev_core_stats_tx_dropped_inc(dev); -- cgit v1.2.3