============================================
WARNING: possible recursive locking detected
5.10.0-syzkaller #0 Not tainted
--------------------------------------------
syz-executor.1/14565 is trying to acquire lock:
ffff888015ab51c8 (&hugetlbfs_i_mmap_rwsem_key){++++}-{3:3}, at: i_mmap_lock_write include/linux/fs.h:493 [inline]
ffff888015ab51c8 (&hugetlbfs_i_mmap_rwsem_key){++++}-{3:3}, at: unmap_ref_private mm/hugetlb.c:4019 [inline]
ffff888015ab51c8 (&hugetlbfs_i_mmap_rwsem_key){++++}-{3:3}, at: hugetlb_cow+0xf55/0x16c0 mm/hugetlb.c:4110

but task is already holding lock:
ffff888015ab51c8 (&hugetlbfs_i_mmap_rwsem_key){++++}-{3:3}, at: i_mmap_lock_read include/linux/fs.h:508 [inline]
ffff888015ab51c8 (&hugetlbfs_i_mmap_rwsem_key){++++}-{3:3}, at: hugetlb_fault+0x2c1/0x24f0 mm/hugetlb.c:4485

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

       CPU0
       ----
  lock(&hugetlbfs_i_mmap_rwsem_key);
  lock(&hugetlbfs_i_mmap_rwsem_key);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by syz-executor.1/14565:
 #0: ffff8880121b4158 (&mm->mmap_lock#2){++++}-{3:3}, at: mmap_read_trylock include/linux/mmap_lock.h:136 [inline]
 #0: ffff8880121b4158 (&mm->mmap_lock#2){++++}-{3:3}, at: do_user_addr_fault+0x25f/0xc60 arch/x86/mm/fault.c:1334
 #1: ffff888015ab51c8 (&hugetlbfs_i_mmap_rwsem_key){++++}-{3:3}, at: i_mmap_lock_read include/linux/fs.h:508 [inline]
 #1: ffff888015ab51c8 (&hugetlbfs_i_mmap_rwsem_key){++++}-{3:3}, at: hugetlb_fault+0x2c1/0x24f0 mm/hugetlb.c:4485
 #2: ffff8880152340f8 (&hugetlb_fault_mutex_table[i]){+.+.}-{3:3}, at: hugetlb_fault+0x433/0x24f0 mm/hugetlb.c:4499

stack backtrace:
CPU: 1 PID: 14565 Comm: syz-executor.1 Not tainted 5.10.0-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+0x115/0x3e6 kernel/locking/lockdep.c:4832
 lock_acquire kernel/locking/lockdep.c:5437 [inline]
 lock_acquire+0x29d/0x750 kernel/locking/lockdep.c:5402
 down_write+0x8d/0x150 kernel/locking/rwsem.c:1406
 i_mmap_lock_write include/linux/fs.h:493 [inline]
 unmap_ref_private mm/hugetlb.c:4019 [inline]
 hugetlb_cow+0xf55/0x16c0 mm/hugetlb.c:4110
 hugetlb_fault+0x1708/0x24f0 mm/hugetlb.c:4562
 handle_mm_fault+0x11b8/0x5760 mm/memory.c:4616
 do_user_addr_fault+0x458/0xc60 arch/x86/mm/fault.c:1393
 handle_page_fault arch/x86/mm/fault.c:1450 [inline]
 exc_page_fault+0x9e/0x180 arch/x86/mm/fault.c:1506
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:580
RIP: 0033:0x445391
Code: 8d 15 53 d8 0d 00 8b 0c 8a 8b 04 82 29 c8 c3 66 2e 0f 1f 84 00 00 00 00 00 48 83 fa 20 48 89 f8 73 77 f6 c2 01 74 0b 0f b6 0e <88> 0f 48 ff c6 48 ff c7 f6 c2 02 74 12 0f b7 0e 66 89 0f 48 83 c6
RSP: 002b:00000000016afbf8 EFLAGS: 00010202
RAX: 00000000200001c0 RBX: 00000000011a07b0 RCX: 0000000000000053
RDX: 000000000000000b RSI: 00000000011a07d0 RDI: 00000000200001c0
RBP: 00000000011a07b8 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000016afcd0 R11: 0000000000000246 R12: fffffffffffffffe
R13: 00000000000737b8 R14: 00000000000003e8 R15: 000000000119c0dc