============================================
WARNING: possible recursive locking detected
5.11.0-rc1-syzkaller #0 Not tainted
--------------------------------------------
syz-executor.3/18130 is trying to acquire lock:
ffff888015230cf8 (&hugetlbfs_i_mmap_rwsem_key){++++}-{3:3}, at: i_mmap_lock_write include/linux/fs.h:493 [inline]
ffff888015230cf8 (&hugetlbfs_i_mmap_rwsem_key){++++}-{3:3}, at: unmap_ref_private mm/hugetlb.c:4019 [inline]
ffff888015230cf8 (&hugetlbfs_i_mmap_rwsem_key){++++}-{3:3}, at: hugetlb_cow+0xedf/0x15f0 mm/hugetlb.c:4110

but task is already holding lock:
ffff888015230cf8 (&hugetlbfs_i_mmap_rwsem_key){++++}-{3:3}, at: i_mmap_lock_read include/linux/fs.h:508 [inline]
ffff888015230cf8 (&hugetlbfs_i_mmap_rwsem_key){++++}-{3:3}, at: hugetlb_fault+0x26c/0x2340 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.3/18130:
 #0: ffff888029915658 (&mm->mmap_lock#2){++++}-{3:3}, at: mmap_read_trylock include/linux/mmap_lock.h:136 [inline]
 #0: ffff888029915658 (&mm->mmap_lock#2){++++}-{3:3}, at: do_user_addr_fault+0x25f/0xc50 arch/x86/mm/fault.c:1334
 #1: ffff888015230cf8 (&hugetlbfs_i_mmap_rwsem_key){++++}-{3:3}, at: i_mmap_lock_read include/linux/fs.h:508 [inline]
 #1: ffff888015230cf8 (&hugetlbfs_i_mmap_rwsem_key){++++}-{3:3}, at: hugetlb_fault+0x26c/0x2340 mm/hugetlb.c:4485
 #2: ffff8880148d6848 (&hugetlb_fault_mutex_table[i]){+.+.}-{3:3}, at: hugetlb_fault+0x368/0x2340 mm/hugetlb.c:4499

stack backtrace:
CPU: 0 PID: 18130 Comm: syz-executor.3 Not tainted 5.11.0-rc1-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+0x15e/0x3b0 kernel/locking/lockdep.c:4832
 lock_acquire kernel/locking/lockdep.c:5437 [inline]
 lock_acquire+0x29d/0x740 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+0xedf/0x15f0 mm/hugetlb.c:4110
 hugetlb_fault+0x1561/0x2340 mm/hugetlb.c:4562
 handle_mm_fault+0x11c3/0x5640 mm/memory.c:4616
 do_user_addr_fault+0x570/0xc50 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: 0010:__put_user_nocheck_8+0x3/0x21
Code: 00 00 48 39 d9 73 34 0f 1f 00 89 01 31 c9 0f 1f 00 c3 66 0f 1f 44 00 00 48 bb f9 ef ff ff ff 7f 00 00 48 39 d9 73 14 0f 1f 00 <48> 89 01 31 c9 0f 1f 00 c3 0f 1f 44 00 00 0f 1f 00 b9 f2 ff ff ff
RSP: 0018:ffffc9000724fe78 EFLAGS: 00010297
RAX: 00000000f55b9ba8 RBX: 00007fffffffeff9 RCX: 0000000020000080
RDX: 1ffff110031fc7b6 RSI: ffffffff8148b2cc RDI: ffff888018fe3db0
RBP: 1ffff92000e49fd2 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000028 R12: 0000000000000000
R13: 0000000020000080 R14: 0000000000000000 R15: ffffffffffffffda
 prctl_get_tid_address kernel/sys.c:2244 [inline]
 __do_sys_prctl+0x8c5/0x1040 kernel/sys.c:2431
 do_syscall_32_irqs_on arch/x86/entry/common.c:78 [inline]
 __do_fast_syscall_32+0x56/0x80 arch/x86/entry/common.c:137
 do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:160
 entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
RIP: 0023:0xf7fbf549
Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000f55b90cc EFLAGS: 00000296 ORIG_RAX: 00000000000000ac
RAX: ffffffffffffffda RBX: 0000000000000028 RCX: 0000000020000080
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000