From 736f16de75f9bb32d76f652cb66f04d1bc685057 Mon Sep 17 00:00:00 2001 From: Dongli Zhang Date: Fri, 4 Mar 2022 06:55:05 -0800 Subject: [PATCH 1/3] net: tap: track dropped skb via kfree_skb_reason() The TAP can be used as vhost-net backend. E.g., the tap_handle_frame() is the interface to forward the skb from TAP to vhost-net/virtio-net. However, there are many "goto drop" in the TAP driver. Therefore, the kfree_skb_reason() is involved at each "goto drop" to help userspace ftrace/ebpf to track the reason for the loss of packets. The below reasons are introduced: - SKB_DROP_REASON_SKB_CSUM - SKB_DROP_REASON_SKB_GSO_SEG - SKB_DROP_REASON_SKB_UCOPY_FAULT - SKB_DROP_REASON_DEV_HDR - SKB_DROP_REASON_FULL_RING Cc: Joao Martins Cc: Joe Jin Signed-off-by: Dongli Zhang Signed-off-by: David S. Miller --- drivers/net/tap.c | 35 +++++++++++++++++++++++++---------- include/linux/skbuff.h | 13 +++++++++++++ include/trace/events/skb.h | 5 +++++ 3 files changed, 43 insertions(+), 10 deletions(-) diff --git a/drivers/net/tap.c b/drivers/net/tap.c index ba2ef5437e167..c3d42062559dd 100644 --- a/drivers/net/tap.c +++ b/drivers/net/tap.c @@ -322,6 +322,7 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb) struct tap_dev *tap; struct tap_queue *q; netdev_features_t features = TAP_FEATURES; + enum skb_drop_reason drop_reason; tap = tap_dev_get_rcu(dev); if (!tap) @@ -343,12 +344,16 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb) struct sk_buff *segs = __skb_gso_segment(skb, features, false); struct sk_buff *next; - if (IS_ERR(segs)) + if (IS_ERR(segs)) { + drop_reason = SKB_DROP_REASON_SKB_GSO_SEG; goto drop; + } if (!segs) { - if (ptr_ring_produce(&q->ring, skb)) + if (ptr_ring_produce(&q->ring, skb)) { + drop_reason = SKB_DROP_REASON_FULL_RING; goto drop; + } goto wake_up; } @@ -356,8 +361,9 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb) skb_list_walk_safe(segs, skb, next) { skb_mark_not_on_list(skb); if (ptr_ring_produce(&q->ring, skb)) { - kfree_skb(skb); - kfree_skb_list(next); + drop_reason = SKB_DROP_REASON_FULL_RING; + kfree_skb_reason(skb, drop_reason); + kfree_skb_list_reason(next, drop_reason); break; } } @@ -369,10 +375,14 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb) */ if (skb->ip_summed == CHECKSUM_PARTIAL && !(features & NETIF_F_CSUM_MASK) && - skb_checksum_help(skb)) + skb_checksum_help(skb)) { + drop_reason = SKB_DROP_REASON_SKB_CSUM; goto drop; - if (ptr_ring_produce(&q->ring, skb)) + } + if (ptr_ring_produce(&q->ring, skb)) { + drop_reason = SKB_DROP_REASON_FULL_RING; goto drop; + } } wake_up: @@ -383,7 +393,7 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb) /* Count errors/drops only here, thus don't care about args. */ if (tap->count_rx_dropped) tap->count_rx_dropped(tap); - kfree_skb(skb); + kfree_skb_reason(skb, drop_reason); return RX_HANDLER_CONSUMED; } EXPORT_SYMBOL_GPL(tap_handle_frame); @@ -632,6 +642,7 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control, int depth; bool zerocopy = false; size_t linear; + enum skb_drop_reason drop_reason; if (q->flags & IFF_VNET_HDR) { vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz); @@ -696,8 +707,10 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control, else err = skb_copy_datagram_from_iter(skb, 0, from, len); - if (err) + if (err) { + drop_reason = SKB_DROP_REASON_SKB_UCOPY_FAULT; goto err_kfree; + } skb_set_network_header(skb, ETH_HLEN); skb_reset_mac_header(skb); @@ -706,8 +719,10 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control, if (vnet_hdr_len) { err = virtio_net_hdr_to_skb(skb, &vnet_hdr, tap_is_little_endian(q)); - if (err) + if (err) { + drop_reason = SKB_DROP_REASON_DEV_HDR; goto err_kfree; + } } skb_probe_transport_header(skb); @@ -738,7 +753,7 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control, return total_len; err_kfree: - kfree_skb(skb); + kfree_skb_reason(skb, drop_reason); err: rcu_read_lock(); diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 2be263184d1ec..67cfff4065b6f 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -412,6 +412,19 @@ enum skb_drop_reason { * this means that L3 protocol is * not supported */ + SKB_DROP_REASON_SKB_CSUM, /* sk_buff checksum computation + * error + */ + SKB_DROP_REASON_SKB_GSO_SEG, /* gso segmentation error */ + SKB_DROP_REASON_SKB_UCOPY_FAULT, /* failed to copy data from + * user space, e.g., via + * zerocopy_sg_from_iter() + * or skb_orphan_frags_rx() + */ + SKB_DROP_REASON_DEV_HDR, /* device driver specific + * header/metadata is invalid + */ + SKB_DROP_REASON_FULL_RING, /* ring buffer is full */ SKB_DROP_REASON_MAX, }; diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h index c0769d943f8ec..240e7e7591fcc 100644 --- a/include/trace/events/skb.h +++ b/include/trace/events/skb.h @@ -51,6 +51,11 @@ EM(SKB_DROP_REASON_XDP, XDP) \ EM(SKB_DROP_REASON_TC_INGRESS, TC_INGRESS) \ EM(SKB_DROP_REASON_PTYPE_ABSENT, PTYPE_ABSENT) \ + EM(SKB_DROP_REASON_SKB_CSUM, SKB_CSUM) \ + EM(SKB_DROP_REASON_SKB_GSO_SEG, SKB_GSO_SEG) \ + EM(SKB_DROP_REASON_SKB_UCOPY_FAULT, SKB_UCOPY_FAULT) \ + EM(SKB_DROP_REASON_DEV_HDR, DEV_HDR) \ + EM(SKB_DROP_REASON_FULL_RING, FULL_RING) \ EMe(SKB_DROP_REASON_MAX, MAX) #undef EM From 45a15d89fbcd280571eba8e5ca309e14ba6afa8f Mon Sep 17 00:00:00 2001 From: Dongli Zhang Date: Fri, 4 Mar 2022 06:55:06 -0800 Subject: [PATCH 2/3] net: tun: split run_ebpf_filter() and pskb_trim() into different "if statement" No functional change. Just to split the if statement into different conditions to use kfree_skb_reason() to trace the reason later. Cc: Joao Martins Cc: Joe Jin Signed-off-by: Dongli Zhang Reviewed-by: David Ahern Signed-off-by: David S. Miller --- drivers/net/tun.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 2a0d8a5d7aec9..6e06c846fe82e 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1086,7 +1086,10 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev) goto drop; len = run_ebpf_filter(tun, skb, len); - if (len == 0 || pskb_trim(skb, len)) + if (len == 0) + goto drop; + + if (pskb_trim(skb, len)) goto drop; if (unlikely(skb_orphan_frags_rx(skb, GFP_ATOMIC))) From 4b4f052e2d89c2eb7e13ee28ba9e85f8097aef3d Mon Sep 17 00:00:00 2001 From: Dongli Zhang Date: Fri, 4 Mar 2022 06:55:07 -0800 Subject: [PATCH 3/3] net: tun: track dropped skb via kfree_skb_reason() The TUN can be used as vhost-net backend. E.g, the tun_net_xmit() is the interface to forward the skb from TUN to vhost-net/virtio-net. However, there are many "goto drop" in the TUN driver. Therefore, the kfree_skb_reason() is involved at each "goto drop" to help userspace ftrace/ebpf to track the reason for the loss of packets. The below reasons are introduced: - SKB_DROP_REASON_DEV_READY - SKB_DROP_REASON_NOMEM - SKB_DROP_REASON_HDR_TRUNC - SKB_DROP_REASON_TAP_FILTER - SKB_DROP_REASON_TAP_TXFILTER Cc: Joao Martins Cc: Joe Jin Signed-off-by: Dongli Zhang Signed-off-by: David S. Miller --- drivers/net/tun.c | 37 ++++++++++++++++++++++++++++--------- include/linux/skbuff.h | 18 ++++++++++++++++++ include/trace/events/skb.h | 5 +++++ 3 files changed, 51 insertions(+), 9 deletions(-) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 6e06c846fe82e..bab92e489fba9 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1058,6 +1058,7 @@ static unsigned int run_ebpf_filter(struct tun_struct *tun, static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev) { struct tun_struct *tun = netdev_priv(dev); + enum skb_drop_reason drop_reason; int txq = skb->queue_mapping; struct netdev_queue *queue; struct tun_file *tfile; @@ -1067,8 +1068,10 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev) tfile = rcu_dereference(tun->tfiles[txq]); /* Drop packet if interface is not attached */ - if (!tfile) + if (!tfile) { + drop_reason = SKB_DROP_REASON_DEV_READY; goto drop; + } if (!rcu_dereference(tun->steering_prog)) tun_automq_xmit(tun, skb); @@ -1078,22 +1081,32 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev) /* Drop if the filter does not like it. * This is a noop if the filter is disabled. * Filter can be enabled only for the TAP devices. */ - if (!check_filter(&tun->txflt, skb)) + if (!check_filter(&tun->txflt, skb)) { + drop_reason = SKB_DROP_REASON_TAP_TXFILTER; goto drop; + } if (tfile->socket.sk->sk_filter && - sk_filter(tfile->socket.sk, skb)) + sk_filter(tfile->socket.sk, skb)) { + drop_reason = SKB_DROP_REASON_SOCKET_FILTER; goto drop; + } len = run_ebpf_filter(tun, skb, len); - if (len == 0) + if (len == 0) { + drop_reason = SKB_DROP_REASON_TAP_FILTER; goto drop; + } - if (pskb_trim(skb, len)) + if (pskb_trim(skb, len)) { + drop_reason = SKB_DROP_REASON_NOMEM; goto drop; + } - if (unlikely(skb_orphan_frags_rx(skb, GFP_ATOMIC))) + if (unlikely(skb_orphan_frags_rx(skb, GFP_ATOMIC))) { + drop_reason = SKB_DROP_REASON_SKB_UCOPY_FAULT; goto drop; + } skb_tx_timestamp(skb); @@ -1104,8 +1117,10 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev) nf_reset_ct(skb); - if (ptr_ring_produce(&tfile->tx_ring, skb)) + if (ptr_ring_produce(&tfile->tx_ring, skb)) { + drop_reason = SKB_DROP_REASON_FULL_RING; goto drop; + } /* NETIF_F_LLTX requires to do our own update of trans_start */ queue = netdev_get_tx_queue(dev, txq); @@ -1122,7 +1137,7 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev) drop: atomic_long_inc(&dev->tx_dropped); skb_tx_error(skb); - kfree_skb(skb); + kfree_skb_reason(skb, drop_reason); rcu_read_unlock(); return NET_XMIT_DROP; } @@ -1720,6 +1735,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, u32 rxhash = 0; int skb_xdp = 1; bool frags = tun_napi_frags_enabled(tfile); + enum skb_drop_reason drop_reason; if (!(tun->flags & IFF_NO_PI)) { if (len < sizeof(pi)) @@ -1823,9 +1839,10 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, if (err) { err = -EFAULT; + drop_reason = SKB_DROP_REASON_SKB_UCOPY_FAULT; drop: atomic_long_inc(&tun->dev->rx_dropped); - kfree_skb(skb); + kfree_skb_reason(skb, drop_reason); if (frags) { tfile->napi.skb = NULL; mutex_unlock(&tfile->napi_mutex); @@ -1872,6 +1889,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, case IFF_TAP: if (frags && !pskb_may_pull(skb, ETH_HLEN)) { err = -ENOMEM; + drop_reason = SKB_DROP_REASON_HDR_TRUNC; goto drop; } skb->protocol = eth_type_trans(skb, tun->dev); @@ -1925,6 +1943,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, if (unlikely(!(tun->dev->flags & IFF_UP))) { err = -EIO; rcu_read_unlock(); + drop_reason = SKB_DROP_REASON_DEV_READY; goto drop; } diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 67cfff4065b6f..34f572271c0c6 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -424,7 +424,25 @@ enum skb_drop_reason { SKB_DROP_REASON_DEV_HDR, /* device driver specific * header/metadata is invalid */ + /* the device is not ready to xmit/recv due to any of its data + * structure that is not up/ready/initialized, e.g., the IFF_UP is + * not set, or driver specific tun->tfiles[txq] is not initialized + */ + SKB_DROP_REASON_DEV_READY, SKB_DROP_REASON_FULL_RING, /* ring buffer is full */ + SKB_DROP_REASON_NOMEM, /* error due to OOM */ + SKB_DROP_REASON_HDR_TRUNC, /* failed to trunc/extract the header + * from networking data, e.g., failed + * to pull the protocol header from + * frags via pskb_may_pull() + */ + SKB_DROP_REASON_TAP_FILTER, /* dropped by (ebpf) filter directly + * attached to tun/tap, e.g., via + * TUNSETFILTEREBPF + */ + SKB_DROP_REASON_TAP_TXFILTER, /* dropped by tx filter implemented + * at tun/tap, e.g., check_filter() + */ SKB_DROP_REASON_MAX, }; diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h index 240e7e7591fcc..e1670e1e49342 100644 --- a/include/trace/events/skb.h +++ b/include/trace/events/skb.h @@ -55,7 +55,12 @@ EM(SKB_DROP_REASON_SKB_GSO_SEG, SKB_GSO_SEG) \ EM(SKB_DROP_REASON_SKB_UCOPY_FAULT, SKB_UCOPY_FAULT) \ EM(SKB_DROP_REASON_DEV_HDR, DEV_HDR) \ + EM(SKB_DROP_REASON_DEV_READY, DEV_READY) \ EM(SKB_DROP_REASON_FULL_RING, FULL_RING) \ + EM(SKB_DROP_REASON_NOMEM, NOMEM) \ + EM(SKB_DROP_REASON_HDR_TRUNC, HDR_TRUNC) \ + EM(SKB_DROP_REASON_TAP_FILTER, TAP_FILTER) \ + EM(SKB_DROP_REASON_TAP_TXFILTER, TAP_TXFILTER) \ EMe(SKB_DROP_REASON_MAX, MAX) #undef EM