============================================
WARNING: possible recursive locking detected
5.11.0-rc7-syzkaller #0 Not tainted
--------------------------------------------
syz-executor.3/10488 is trying to acquire lock:
ffff888061993220 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1598 [inline]
ffff888061993220 (sk_lock-AF_INET6){+.+.}-{0:0}, at: inet_stream_connect+0x3f/0xa0 net/ipv4/af_inet.c:724

but task is already holding lock:
ffff88805b753120
 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1598 [inline]
 (sk_lock-AF_INET6){+.+.}-{0:0}, at: mptcp_stream_connect+0x85/0x800 net/mptcp/protocol.c:3171

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

       CPU0
       ----
  lock(sk_lock-AF_INET6);
  lock(sk_lock-AF_INET6);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

1 lock held by syz-executor.3/10488:
 #0: ffff88805b753120 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1598 [inline]
 #0: ffff88805b753120 (sk_lock-AF_INET6){+.+.}-{0:0}, at: mptcp_stream_connect+0x85/0x800 net/mptcp/protocol.c:3171

stack backtrace:
CPU: 1 PID: 10488 Comm: syz-executor.3 Not tainted 5.11.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:120
 print_deadlock_bug kernel/locking/lockdep.c:2761 [inline]
 check_deadlock kernel/locking/lockdep.c:2804 [inline]
 validate_chain kernel/locking/lockdep.c:3595 [inline]
 __lock_acquire.cold+0x114/0x39e kernel/locking/lockdep.c:4832
 lock_acquire kernel/locking/lockdep.c:5442 [inline]
 lock_acquire+0x1a8/0x720 kernel/locking/lockdep.c:5407
 lock_sock_nested+0xc5/0x110 net/core/sock.c:3071
 lock_sock include/net/sock.h:1598 [inline]
 inet_stream_connect+0x3f/0xa0 net/ipv4/af_inet.c:724
 mptcp_stream_connect+0x156/0x800 net/mptcp/protocol.c:3200
 __sys_connect_file+0x155/0x1a0 net/socket.c:1835
 __sys_connect+0x161/0x190 net/socket.c:1852
 __do_sys_connect net/socket.c:1862 [inline]
 __se_sys_connect net/socket.c:1859 [inline]
 __x64_sys_connect+0x6f/0xb0 net/socket.c:1859
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x465d99
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 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f83a02e3188 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 000000000056c0b0 RCX: 0000000000465d99
RDX: 000000000000001c RSI: 0000000020000000 RDI: 0000000000000003
RBP: 00000000004bcf27 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056c0b0
R13: 00007fff2d67455f R14: 00007f83a02e3300 R15: 0000000000022000