======================================================
WARNING: possible circular locking dependency detected
5.12.0-rc5-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.1/30642 is trying to acquire lock:
ffffffff8d66b1a8 (rtnl_mutex){+.+.}-{3:3}, at: ipv6_sock_ac_close+0xd5/0x110 net/ipv6/anycast.c:219

but task is already holding lock:
ffff8880734f6d20 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1600 [inline]
ffff8880734f6d20 (sk_lock-AF_INET6){+.+.}-{0:0}, at: mptcp6_release+0x57/0x130 net/mptcp/protocol.c:3550

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (sk_lock-AF_INET6){+.+.}-{0:0}:
       lock_sock_nested+0xca/0x120 net/core/sock.c:3071
       lock_sock include/net/sock.h:1600 [inline]
       do_ipv6_setsockopt.constprop.0+0x31f/0x41f0 net/ipv6/ipv6_sockglue.c:418
       ipv6_setsockopt+0xd6/0x180 net/ipv6/ipv6_sockglue.c:1003
       rawv6_setsockopt+0xd8/0x690 net/ipv6/raw.c:1081
       __sys_setsockopt+0x2db/0x610 net/socket.c:2117
       __do_sys_setsockopt net/socket.c:2128 [inline]
       __se_sys_setsockopt net/socket.c:2125 [inline]
       __x64_sys_setsockopt+0xba/0x150 net/socket.c:2125
       do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
       entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #0 (rtnl_mutex){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:2936 [inline]
       check_prevs_add kernel/locking/lockdep.c:3059 [inline]
       validate_chain kernel/locking/lockdep.c:3674 [inline]
       __lock_acquire+0x2b14/0x54c0 kernel/locking/lockdep.c:4900
       lock_acquire kernel/locking/lockdep.c:5510 [inline]
       lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5475
       __mutex_lock_common kernel/locking/mutex.c:949 [inline]
       __mutex_lock+0x139/0x1120 kernel/locking/mutex.c:1096
       ipv6_sock_ac_close+0xd5/0x110 net/ipv6/anycast.c:219
       mptcp6_release+0xc1/0x130 net/mptcp/protocol.c:3559
       __sock_release+0xcd/0x280 net/socket.c:599
       sock_close+0x18/0x20 net/socket.c:1258
       __fput+0x288/0x920 fs/file_table.c:280
       task_work_run+0xdd/0x1a0 kernel/task_work.c:140
       tracehook_notify_resume include/linux/tracehook.h:189 [inline]
       exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
       exit_to_user_mode_prepare+0x249/0x250 kernel/entry/common.c:208
       __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
       syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:301
       entry_SYSCALL_64_after_hwframe+0x44/0xae

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(sk_lock-AF_INET6);
                               lock(rtnl_mutex);
                               lock(sk_lock-AF_INET6);
  lock(rtnl_mutex);

 *** DEADLOCK ***

2 locks held by syz-executor.1/30642:
 #0: ffff888086cd4c90 (&sb->s_type->i_mutex_key#13){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:775 [inline]
 #0: ffff888086cd4c90 (&sb->s_type->i_mutex_key#13){+.+.}-{3:3}, at: __sock_release+0x86/0x280 net/socket.c:598
 #1: ffff8880734f6d20 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1600 [inline]
 #1: ffff8880734f6d20 (sk_lock-AF_INET6){+.+.}-{0:0}, at: mptcp6_release+0x57/0x130 net/mptcp/protocol.c:3550

stack backtrace:
CPU: 1 PID: 30642 Comm: syz-executor.1 Not tainted 5.12.0-rc5-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+0x141/0x1d7 lib/dump_stack.c:120
 check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2127
 check_prev_add kernel/locking/lockdep.c:2936 [inline]
 check_prevs_add kernel/locking/lockdep.c:3059 [inline]
 validate_chain kernel/locking/lockdep.c:3674 [inline]
 __lock_acquire+0x2b14/0x54c0 kernel/locking/lockdep.c:4900
 lock_acquire kernel/locking/lockdep.c:5510 [inline]
 lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5475
 __mutex_lock_common kernel/locking/mutex.c:949 [inline]
 __mutex_lock+0x139/0x1120 kernel/locking/mutex.c:1096
 ipv6_sock_ac_close+0xd5/0x110 net/ipv6/anycast.c:219
 mptcp6_release+0xc1/0x130 net/mptcp/protocol.c:3559
 __sock_release+0xcd/0x280 net/socket.c:599
 sock_close+0x18/0x20 net/socket.c:1258
 __fput+0x288/0x920 fs/file_table.c:280
 task_work_run+0xdd/0x1a0 kernel/task_work.c:140
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x249/0x250 kernel/entry/common.c:208
 __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
 syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:301
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x41926b
Code: 0f 05 48 3d 00 f0 ff ff 77 45 c3 0f 1f 40 00 48 83 ec 18 89 7c 24 0c e8 63 fc ff ff 8b 7c 24 0c 41 89 c0 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 35 44 89 c7 89 44 24 0c e8 a1 fc ff ff 8b 44
RSP: 002b:0000000000a9fb80 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 000000000041926b
RDX: 0000000000000000 RSI: 000000000d1147dc RDI: 0000000000000003
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000001b30428adc
R10: 0000000000000000 R11: 0000000000000293 R12: 000000000056c9e0
R13: 000000000056c9e0 R14: 000000000056bf60 R15: 0000000000206dd5