[PATCH] tipc: defer local Nagle backlog xmit from receive path
From: "syzbot" <syzbot@kernel.org>
Date: 2026-08-12 13:00:50
Also in:
lkml, syzbot
Subsystem:
networking [general], the rest, tipc network layer · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, Jon Maloy
From: Bartosz Chronowski <redacted>
A local TIPC stream socket workload can trap a CPU in an endless receive
loop. The resulting soft lockup can make the system unavailable.
tipc_sk_push_backlog() can transmit delayed stream data while tipc_sk_rcv()
holds a destination socket's sk_lock.slock. Own-node transmission enters
tipc_sk_rcv() synchronously. A reply that reaches the ancestor socket
cannot acquire the still-held lock, and tipc_sk_rcv() retries without
consuming its input queue.
Pass the receive output queue to tipc_sk_push_backlog() from receive-side
callers. Queue own-node output there so the enclosing receive path sends it
after releasing the socket lock. Keep shutdown and remote-node transmission
on the existing direct path, preserving remote link congestion handling.
Fixes: c0bceb97db9e ("tipc: add smart nagle feature")
Assisted-by: Gemini:gemini-3.5-flash Gemini:gemini-3.1-pro-preview syzbot
Reported-by: syzbot+10a41dc44eef71aa9450@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=10a41dc44eef71aa9450
Link: https://syzkaller.appspot.com/ai_job?id=aa2dc129-33d3-42e7-bd0b-bf2198c9c9c2
Signed-off-by: Bartosz Chronowski <redacted>
---diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index e564341e0..33d744dc5 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c@@ -156,7 +156,8 @@ static int tipc_sk_insert(struct tipc_sock *tsk); static void tipc_sk_remove(struct tipc_sock *tsk); static int __tipc_sendstream(struct socket *sock, struct msghdr *m, size_t dsz); static int __tipc_sendmsg(struct socket *sock, struct msghdr *m, size_t dsz); -static void tipc_sk_push_backlog(struct tipc_sock *tsk, bool nagle_ack); +static void tipc_sk_push_backlog(struct tipc_sock *tsk, bool nagle_ack, + struct sk_buff_head *xmitq); static int tipc_wait_for_connect(struct socket *sock, long *timeo_p); static const struct proto_ops packet_ops;
@@ -560,7 +561,7 @@ static void __tipc_shutdown(struct socket *sock, int error) !tsk_conn_cong(tsk))); /* Push out delayed messages if in Nagle mode */ - tipc_sk_push_backlog(tsk, false); + tipc_sk_push_backlog(tsk, false, NULL); /* Remove pending SYN */ __skb_queue_purge(&sk->sk_write_queue);
@@ -1267,8 +1268,10 @@ void tipc_sk_mcast_rcv(struct net *net, struct sk_buff_head *arrvq, /* tipc_sk_push_backlog(): send accumulated buffers in socket write queue * when socket is in Nagle mode + * @xmitq: receive output queue, or NULL outside receive context */ -static void tipc_sk_push_backlog(struct tipc_sock *tsk, bool nagle_ack) +static void tipc_sk_push_backlog(struct tipc_sock *tsk, bool nagle_ack, + struct sk_buff_head *xmitq) { struct sk_buff_head *txq = &tsk->sk.sk_write_queue; struct sk_buff *skb = skb_peek_tail(txq);
@@ -1310,6 +1313,12 @@ static void tipc_sk_push_backlog(struct tipc_sock *tsk, bool nagle_ack) tsk->pkt_cnt += skb_queue_len(txq); tsk->snt_unacked += tsk->snd_backlog; tsk->snd_backlog = 0; + + if (xmitq && in_own_node(net, dnode)) { + skb_queue_splice_tail_init(txq, xmitq); + return; + } + rc = tipc_node_xmit(net, txq, dnode, tsk->portid); if (rc == -ELINKCONG) tsk->cong_link_cnt = 1;
@@ -1367,7 +1376,7 @@ static void tipc_sk_conn_proto_rcv(struct tipc_sock *tsk, struct sk_buff *skb, goto exit; was_cong = tsk_conn_cong(tsk); - tipc_sk_push_backlog(tsk, msg_nagle_ack(hdr)); + tipc_sk_push_backlog(tsk, msg_nagle_ack(hdr), xmitq); tsk->snt_unacked -= msg_conn_ack(hdr); if (tsk->peer_caps & TIPC_BLOCK_FLOWCTL) tsk->snd_win = msg_adv_win(hdr);
@@ -2165,7 +2174,7 @@ static void tipc_sk_proto_rcv(struct sock *sk, smp_wmb(); tsk->cong_link_cnt--; wakeup = true; - tipc_sk_push_backlog(tsk, false); + tipc_sk_push_backlog(tsk, false, xmitq); break; case GROUP_PROTOCOL: tipc_group_proto_rcv(grp, &wakeup, hdr, inputq, xmitq);
@@ -2256,7 +2265,7 @@ static bool tipc_sk_filter_connect(struct tipc_sock *tsk, struct sk_buff *skb, return false; case TIPC_ESTABLISHED: if (!skb_queue_empty(&sk->sk_write_queue)) - tipc_sk_push_backlog(tsk, false); + tipc_sk_push_backlog(tsk, false, xmitq); /* Accept only connection-based messages sent by peer */ if (likely(con_msg && !err && pport == oport && pnode == onode)) {
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