syzbot

============================================
WARNING: possible recursive locking detected
6.13.0-rc6-next-20250107-syzkaller #0 Not tainted
--------------------------------------------
syz-executor213/5832 is trying to acquire lock:
ffff8880790b35c8 (vm_lock){++++}-{0:0}, at: uffd_move_lock mm/userfaultfd.c:1477 [inline]
ffff8880790b35c8 (vm_lock){++++}-{0:0}, at: move_pages+0x26b/0x1680 mm/userfaultfd.c:1632

but task is already holding lock:
ffff8880790b3488 (vm_lock){++++}-{0:0}, at: vma_start_read_locked include/linux/mm.h:808 [inline]
ffff8880790b3488 (vm_lock){++++}-{0:0}, at: uffd_lock_vma+0x20c/0x2c0 mm/userfaultfd.c:88

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

       CPU0
       ----
  lock(vm_lock);
  lock(vm_lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syz-executor213/5832:
 #0: ffff8880790b3488 (vm_lock){++++}-{0:0}, at: vma_start_read_locked include/linux/mm.h:808 [inline]
 #0: ffff8880790b3488 (vm_lock){++++}-{0:0}, at: uffd_lock_vma+0x20c/0x2c0 mm/userfaultfd.c:88
 #1: ffffffff8e937ee0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:337 [inline]
 #1: ffffffff8e937ee0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #1: ffffffff8e937ee0 (rcu_read_lock){....}-{1:3}, at: lock_vma_under_rcu+0x1dd/0x9a0 mm/memory.c:6431

stack backtrace:
CPU: 1 UID: 0 PID: 5832 Comm: syz-executor213 Not tainted 6.13.0-rc6-next-20250107-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_deadlock_bug+0x483/0x620 kernel/locking/lockdep.c:3039
 check_deadlock kernel/locking/lockdep.c:3091 [inline]
 validate_chain+0x15e2/0x5920 kernel/locking/lockdep.c:3893
 __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5228
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
 vma_start_read include/linux/mm.h:749 [inline]
 lock_vma_under_rcu+0x35f/0x9a0 mm/memory.c:6436
 uffd_move_lock mm/userfaultfd.c:1477 [inline]
 move_pages+0x26b/0x1680 mm/userfaultfd.c:1632
 userfaultfd_move fs/userfaultfd.c:1899 [inline]
 userfaultfd_ioctl+0x5221/0x6840 fs/userfaultfd.c:2022
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0xf5/0x170 fs/ioctl.c:892
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb464fd9329
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd69c11768 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007ffd69c11938 RCX: 00007fb464fd9329
RDX: 0000000020000040 RSI: 00000