============================================
WARNING: possible recursive locking detected
6.11.0-rc7-syzkaller #0 Not tainted
--------------------------------------------
syz.0.0/5111 is trying to acquire lock:
ffff88804c251958 (k-slock-AF_INET){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff88804c251958 (k-slock-AF_INET){+.-.}-{2:2}, at: sk_clone_lock+0x2cd/0xf40 net/core/sock.c:2328

but task is already holding lock:
ffff888040027018 (k-slock-AF_INET){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff888040027018 (k-slock-AF_INET){+.-.}-{2:2}, at: sk_clone_lock+0x2cd/0xf40 net/core/sock.c:2328

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(k-slock-AF_INET);
  lock(k-slock-AF_INET);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

7 locks held by syz.0.0/5111:
 #0: ffff88804c250e18 (sk_lock-AF_INET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1607 [inline]
 #0: ffff88804c250e18 (sk_lock-AF_INET){+.+.}-{0:0}, at: inet_stream_connect+0x50/0xa0 net/ipv4/af_inet.c:749
 #1: ffff888040026458 (k-sk_lock-AF_INET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1607 [inline]
 #1: ffff888040026458 (k-sk_lock-AF_INET){+.+.}-{0:0}, at: mptcp_connect+0x501/0x920 net/mptcp/protocol.c:3762
 #2: ffffffff8e938320 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:326 [inline]
 #2: ffffffff8e938320 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
 #2: ffffffff8e938320 (rcu_read_lock){....}-{1:2}, at: __ip_queue_xmit+0x5f/0x1b80 net/ipv4/ip_output.c:470
 #3: ffffffff8e938320 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:326 [inline]
 #3: ffffffff8e938320 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
 #3: ffffffff8e938320 (rcu_read_lock){....}-{1:2}, at: ip_finish_output2+0x45f/0x1390 net/ipv4/ip_output.c:228
 #4: ffffffff8e938320 (rcu_read_lock){....}-{1:2}, at: local_lock_acquire include/linux/local_lock_internal.h:29 [inline]
 #4: ffffffff8e938320 (rcu_read_lock){....}-{1:2}, at: process_backlog+0x33b/0x15b0 net/core/dev.c:6104
 #5: ffffffff8e938320 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:326 [inline]
 #5: ffffffff8e938320 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
 #5: ffffffff8e938320 (rcu_read_lock){....}-{1:2}, at: ip_local_deliver_finish+0x230/0x5f0 net/ipv4/ip_input.c:232
 #6: ffff888040027018 (k-slock-AF_INET){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
 #6: ffff888040027018 (k-slock-AF_INET){+.-.}-{2:2}, at: sk_clone_lock+0x2cd/0xf40 net/core/sock.c:2328

stack backtrace:
CPU: 0 UID: 0 PID: 5111 Comm: syz.0.0 Not tainted 6.11.0-rc7-syzkaller #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:93 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:119
 check_deadlock kernel/locking/lockdep.c:3061 [inline]
 validate_chain+0x15d3/0x5900 kernel/locking/lockdep.c:3855
 __lock_acquire+0x137a/0x2040 kernel/locking/lockdep.c:5142
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5759
 __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
 _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
 spin_lock include/linux/spinlock.h:351 [inline]
 sk_clone_lock+0x2cd/0xf40 net/core/sock.c:2328
 mptcp_sk_clone_init+0x32/0x13c0 net/mptcp/protocol.c:3279
 subflow_syn_recv_sock+0x931/0x1920 net/mptcp/subflow.c:874
 tcp_check_req+0xfe4/0x1a20 net/ipv4/tcp_minisocks.c:853
 tcp_v4_rcv+0x1c3e/0x37f0 net/ipv4/tcp_ipv4.c:2267
 ip_protocol_deliver_rcu+0x22e/0x440 net/ipv4/ip_input.c:205
 ip_local_deliver_finish+0x341/0x5f0 net/ipv4/ip_input.c:233
 NF_HOOK+0x3a4/0x450 include/linux/netfilter.h:314
 NF_HOOK+0x3a4/0x450 include/linux/netfilter.h:314
 __netif_receive_skb_one_core net/core/dev.c:5661 [inline]
 __netif_receive_skb+0x2bf/0x650 net/core/dev.c:5775
 process_backlog+0x662/0x15b0 net/core/dev.c:6108
 __napi_poll+0xcb/0x490 net/core/dev.c:6772
 napi_poll net/core/dev.c:6841 [inline]
 net_rx_action+0x89b/0x1240 net/core/dev.c:6963
 handle_softirqs+0x2c4/0x970 kernel/softirq.c:554
 do_softirq+0x11b/0x1e0 kernel/softirq.c:455
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0x1bb/0x200 kernel/softirq.c:382
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 rcu_read_unlock_bh include/linux/rcupdate.h:908 [inline]
 __dev_queue_xmit+0x1763/0x3e90 net/core/dev.c:4450
 dev_queue_xmit include/linux/netdevice.h:3105 [inline]
 neigh_hh_output include/net/neighbour.h:526 [inline]
 neigh_output include/net/neighbour.h:540 [inline]
 ip_finish_output2+0xd41/0x1390 net/ipv4/ip_output.c:235
 ip_local_out net/ipv4/ip_output.c:129 [inline]
 __ip_queue_xmit+0x118c/0x1b80 net/ipv4/ip_output.c:535
 __tcp_transmit_skb+0x2544/0x3b30 net/ipv4/tcp_output.c:1466
 tcp_rcv_synsent_state_process net/ipv4/tcp_input.c:6542 [inline]
 tcp_rcv_state_process+0x2c32/0x4570 net/ipv4/tcp_input.c:6729
 tcp_v4_do_rcv+0x77d/0xc70 net/ipv4/tcp_ipv4.c:1934
 sk_backlog_rcv include/net/sock.h:1111 [inline]
 __release_sock+0x214/0x350 net/core/sock.c:3004
 release_sock+0x61/0x1f0 net/core/sock.c:3558
 mptcp_connect+0x68b/0x920 net/mptcp/protocol.c:3784
 __inet_stream_connect+0x262/0xf30 net/ipv4/af_inet.c:679
 inet_stream_connect+0x65/0xa0 net/ipv4/af_inet.c:750
 __sys_connect_file net/socket.c:2061 [inline]
 __sys_connect+0x2df/0x310 net/socket.c:2078
 __do_sys_connect net/socket.c:2088 [inline]
 __se_sys_connect net/socket.c:2085 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:2085
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fda1197cef9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fda1269c038 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007fda11b35f80 RCX: 00007fda1197cef9
RDX: 0000000000000010 RSI: 0000000020000000 RDI: 000000000000000c
RBP: 00007fda119ef046 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fda11b35f80 R15: 00007ffe8f850da8
 </TASK>