bisecting fixing commit since 29ce8f9701072fc221d9c38ad952de1a9578f95c
building syzkaller on 7eb7e15259fddd67759f90feb2b016da878f76c7
testing commit 29ce8f9701072fc221d9c38ad952de1a9578f95c
compiler: gcc (GCC) 10.2.1 20210217, GNU ld (GNU Binutils for Debian) 2.35.2
kernel signature: a43f9fd0c03116b5a7fbbe98af2dbf1003bf57525103af08f68122df7c7566cb
all runs: crashed: INFO: task hung in lock_sock_nested
testing current HEAD 5833291ab6de9c3e2374336b51c814e515e8f3a5
testing commit 5833291ab6de9c3e2374336b51c814e515e8f3a5
compiler: gcc (GCC) 10.2.1 20210217, GNU ld (GNU Binutils for Debian) 2.35.2
kernel signature: 30910e4425bbe420e9c414d5764a126c390d59a49e96872dfd8018b60702aa8b
all runs: crashed: possible deadlock in rfcomm_sk_state_change
revisions tested: 2, total time: 22m49.562742857s (build: 12m29.796884478s, test: 9m42.77149799s)
the crash still happens on HEAD
commit msg: Merge tag 'pci-v5.16-fixes-1' of git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci
crash: possible deadlock in rfcomm_sk_state_change
============================================
WARNING: possible recursive locking detected
5.15.0-syzkaller #0 Not tainted
--------------------------------------------
syz-executor.2/9083 is trying to acquire lock:
ffff88807b793120 (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1645 [inline]
ffff88807b793120 (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}, at: rfcomm_sk_state_change+0x99/0x320 net/bluetooth/rfcomm/sock.c:73

but task is already holding lock:
ffff88807b793120 (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1645 [inline]
ffff88807b793120 (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}, at: rfcomm_sock_shutdown+0x41/0x1b0 net/bluetooth/rfcomm/sock.c:902

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

       CPU0
       ----
  lock(sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM);
  lock(sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM
);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

4 locks held by syz-executor.2/9083:
 #0: ffff88806053d610 (&sb->s_type->i_mutex_key#13
){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:783 [inline]
){+.+.}-{3:3}, at: __sock_release+0x76/0x270 net/socket.c:648
 #1: ffff88807b793120
 (
sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM
){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1645 [inline]
){+.+.}-{0:0}, at: rfcomm_sock_shutdown+0x41/0x1b0 net/bluetooth/rfcomm/sock.c:902
 #2: ffffffff8c462ce8 (rfcomm_mutex){+.+.}-{3:3}, at: rfcomm_dlc_close+0x25/0x200 net/bluetooth/rfcomm/core.c:507
 #3: ffff888073d94d28 (&d->lock){+.+.}-{3:3}, at: __rfcomm_dlc_close+0xff/0x770 net/bluetooth/rfcomm/core.c:487

stack backtrace:
CPU: 1 PID: 9083 Comm: syz-executor.2 Not tainted 5.15.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x57/0x7d lib/dump_stack.c:106
 print_deadlock_bug kernel/locking/lockdep.c:2956 [inline]
 check_deadlock kernel/locking/lockdep.c:2999 [inline]
 validate_chain kernel/locking/lockdep.c:3788 [inline]
 __lock_acquire.cold+0x229/0x3ab kernel/locking/lockdep.c:5027
 lock_acquire kernel/locking/lockdep.c:5637 [inline]
 lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5602
 lock_sock_nested+0x2b/0xd0 net/core/sock.c:3285
 lock_sock include/net/sock.h:1645 [inline]
 rfcomm_sk_state_change+0x99/0x320 net/bluetooth/rfcomm/sock.c:73
 __rfcomm_dlc_close+0x153/0x770 net/bluetooth/rfcomm/core.c:489
 rfcomm_dlc_close+0x1a4/0x200 net/bluetooth/rfcomm/core.c:520
 __rfcomm_sock_close+0x80/0x1f0 net/bluetooth/rfcomm/sock.c:220
 rfcomm_sock_shutdown+0xb1/0x1b0 net/bluetooth/rfcomm/sock.c:905
 rfcomm_sock_release+0x4a/0x120 net/bluetooth/rfcomm/sock.c:925
 __sock_release+0xbb/0x270 net/socket.c:649
 sock_close+0xf/0x20 net/socket.c:1314
 __fput+0x204/0x8d0 fs/file_table.c:280
 task_work_run+0xc0/0x160 kernel/task_work.c:164
 get_signal+0x158d/0x1ce0 kernel/signal.c:2602
 arch_do_signal_or_restart+0x2a9/0x1c40 arch/x86/kernel/signal.c:868
 handle_signal_work kernel/entry/common.c:148 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
 exit_to_user_mode_prepare+0x17d/0x290 kernel/entry/common.c:207
 __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
 syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:300
 do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x4665f9
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:00007fcd33a21188 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: fffffffffffffffc RBX: 000000000056bf80 RCX: 00000000004665f9
RDX: 0000000000000080 RSI: 0000000020000000 RDI: 0000000000000004
RBP: 00000000004bfcc4 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf80
R13: 00007ffc6c79805f R14: 00007fcd33a21300 R15: 0000000000022000
 </TASK>