Syzkaller was able to trigger again the following splat: WARNING: CPU: 1 PID: 12512 at net/mptcp/protocol.c:761 mptcp_reset_timer+0x12a/0x160 net/mptcp/protocol.c:761 Modules linked in: CPU: 1 PID: 12512 Comm: kworker/1:6 Not tainted 5.10.0-rc6 #52 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014 Workqueue: events mptcp_worker RIP: 0010:mptcp_reset_timer+0x12a/0x160 net/mptcp/protocol.c:761 Code: e8 4b 0c ad ff e8 56 21 88 fe 48 b8 00 00 00 00 00 fc ff df 48 c7 04 03 00 00 00 00 48 83 c4 40 5b 5d 41 5c c3 e8 36 21 88 fe <0f> 0b 41 bc c8 00 00 00 eb 98 e8 e7 b1 af fe e9 30 ff ff ff 48 c7 RSP: 0018:ffffc900018c7c68 EFLAGS: 00010293 RAX: ffff888108cb1c80 RBX: 1ffff92000318f8d RCX: ffffffff82ad0307 RDX: 0000000000000000 RSI: ffffffff82ad036a RDI: 0000000000000007 RBP: ffff888113e2d000 R08: ffff888108cb1c80 R09: ffffed10227c5ab7 R10: ffff888113e2d5b7 R11: ffffed10227c5ab6 R12: 0000000000000000 R13: ffff88801f100000 R14: ffff888113e2d5b0 R15: 0000000000000001 FS: 0000000000000000(0000) GS:ffff88811b500000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fd76a874ef8 CR3: 000000001689c005 CR4: 0000000000170ee0 Call Trace: mptcp_worker+0xaa4/0x1560 net/mptcp/protocol.c:2334 process_one_work+0x8d3/0x1200 kernel/workqueue.c:2272 worker_thread+0x9c/0x1090 kernel/workqueue.c:2418 kthread+0x303/0x410 kernel/kthread.c:292 ret_from_fork+0x22/0x30 arch/x86/entry/entry_64.S:296 The mptcp_worker tries to update the MPTCP retransmission timer even if such timer is not currently scheduled. mptcp_check_data_fin_ack() can clear the rtx timer just before mptcp_rtx_head(), but leaving data in the rtx queue - that will be cleared at msk sock release_cb time. The above may additionally cause spurious, unneeded MPTCP-level retransissions. Fix the issue adding explicit clearing the rtx queue before trying to retransmit and dropping the unneeded timer stop. Additionally drop the unused mptcp_rtx_head() helper. Reported-by: Christoph Paasch <cpaasch(a)apple.com&gt; Fixes: 6e628cd3a8f7 ("mptcp: use mptcp release_cb for delayed tasks") Signed-off-by: Paolo Abeni <pabeni(a)redhat.com&gt; --- Note: I hope this should fix https://github.com/multipath-tcp/mptcp_net-next/issues/126 @Christoph could you please give this one a spin? --- net/mptcp/protocol.c | 3 +-- net/mptcp/protocol.h | 10 ---------- 2 files changed, 1 insertion(+), 12 deletions(-) diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index 305d25cbc216a..88a6fb6f7ecc8 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -363,8 +363,6 @@ static void mptcp_check_data_fin_ack(struct sock *sk) /* Look for an acknowledged DATA_FIN */ if (mptcp_pending_data_fin_ack(sk)) { - mptcp_stop_timer(sk); - WRITE_ONCE(msk->snd_data_fin_enable, 0); switch (sk->sk_state) { @@ -2270,6 +2268,7 @@ static void mptcp_worker(struct work_struct *work) if (!test_and_clear_bit(MPTCP_WORK_RTX, &msk->flags)) goto unlock; + __mptcp_clean_una(sk); dfrag = mptcp_rtx_head(sk); if (!dfrag) goto unlock; diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h index 1024ea1512d2b..1bb44a4baf4a5 100644 --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -335,16 +335,6 @@ static inline struct mptcp_data_frag *mptcp_pending_tail(const struct sock *sk) return list_last_entry(&msk->rtx_queue, struct mptcp_data_frag, list); } -static inline struct mptcp_data_frag *mptcp_rtx_tail(const struct sock *sk) -{ - struct mptcp_sock *msk = mptcp_sk(sk); - - if (!before64(msk->snd_nxt, READ_ONCE(msk->snd_una))) - return NULL; - - return list_last_entry(&msk->rtx_queue, struct mptcp_data_frag, list); -} - static inline struct mptcp_data_frag *mptcp_rtx_head(const struct sock *sk) { struct mptcp_sock *msk = mptcp_sk(sk); -- 2.26.2