============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
kworker/u4:2/37 is trying to acquire lock:
ffff888040f500a8 (&tree->tree_lock/1){+.+.}-{4:4}, at: hfs_find_init+0x18d/0x300 fs/hfs/bfind.c:-1

but task is already holding lock:
ffff888040f500a8 (&tree->tree_lock/1){+.+.}-{4:4}, at: hfs_find_init+0x18d/0x300 fs/hfs/bfind.c:-1

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

       CPU0
       ----
  lock(&tree->tree_lock/1);
  lock(&tree->tree_lock/1);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

locks held by kworker/u4:2/37: 5, last CPU#0:
 #0: ffff88801dbb5148 ((wq_completion)writeback){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline]
 #0: ffff88801dbb5148 ((wq_completion)writeback){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #0: ffff88801dbb5148 ((wq_completion)writeback){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3460 [inline]
 #0: ffff88801dbb5148 ((wq_completion)writeback){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 kernel/workqueue.c:3578
 #1: ffffc900003f7c40 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline]
 #1: ffffc900003f7c40 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #1: ffffc900003f7c40 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3460 [inline]
 #1: ffffc900003f7c40 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 kernel/workqueue.c:3578
 #2: ffff8880345360e8 (&type->s_umount_key#53){.+.+}-{4:4}, at: super_trylock_shared+0x23/0xf0 fs/super.c:670
 #3: ffff888040f500a8 (&tree->tree_lock/1){+.+.}-{4:4}, at: hfs_find_init+0x18d/0x300 fs/hfs/bfind.c:-1
 #4: ffff8880539400a0 (&HFS_I(tree->inode)->extents_lock){+.+.}-{4:4}, at: hfs_extend_file+0xf9/0x1680 fs/hfs/extent.c:403

stack backtrace:
CPU: 0 UID: 0 PID: 37 Comm: kworker/u4:2 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Workqueue: writeback wb_workfn (flush-7:0)
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_deadlock_bug+0x27a/0x290 kernel/locking/lockdep.c:3085
 check_deadlock kernel/locking/lockdep.c:3137 [inline]
 validate_chain kernel/locking/lockdep.c:3939 [inline]
 __lock_acquire+0x25db/0x2de0 kernel/locking/lockdep.c:5288
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x197/0x15a0 kernel/locking/mutex.c:821
 hfs_find_init+0x18d/0x300 fs/hfs/bfind.c:-1
 hfs_ext_read_extent fs/hfs/extent.c:206 [inline]
 hfs_extend_file+0x367/0x1680 fs/hfs/extent.c:407
 hfs_bmap_reserve+0x108/0x430 fs/hfs/btree.c:402
 __hfs_ext_write_extent+0x200/0x620 fs/hfs/extent.c:121
 hfs_ext_write_extent+0x17d/0x210 fs/hfs/extent.c:150
 hfs_write_inode+0x117/0xa00 fs/hfs/inode.c:475
 write_inode fs/fs-writeback.c:1620 [inline]
 __writeback_single_inode+0x69d/0x1220 fs/fs-writeback.c:1863
 writeback_sb_inodes+0x9de/0x1af0 fs/fs-writeback.c:2111
 __writeback_inodes_wb+0x114/0x240 fs/fs-writeback.c:2187
 wb_writeback+0x42f/0xad0 fs/fs-writeback.c:2298
 wb_check_start_all fs/fs-writeback.c:2424 [inline]
 wb_do_writeback fs/fs-writeback.c:2471 [inline]
 wb_workfn+0x980/0x10f0 fs/fs-writeback.c:2509
 process_one_work kernel/workqueue.c:3495 [inline]
 process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659
 kthread+0x38b/0x480 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>