Re: [syzbot] possible deadlock in ovl_fallocate

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syzbot has found a reproducer for the following issue on:

HEAD commit:    591cd61541b9 Add linux-next specific files for 20221207
git tree:       linux-next
kernel config:
dashboard link:
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:
C reproducer:

Downloadable assets:
disk image:
kernel image:

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+38a94e1872470e3450a6@xxxxxxxxxxxxxxxxxxxxxxxxx

WARNING: possible recursive locking detected
6.1.0-rc8-next-20221207-syzkaller #0 Not tainted
syz-executor169/5069 is trying to acquire lock:
ffff8880750fa480 (&ovl_i_mutex_key[depth]){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:756 [inline]
ffff8880750fa480 (&ovl_i_mutex_key[depth]){+.+.}-{3:3}, at: ovl_remove_privs_unlocked fs/overlayfs/file.c:519 [inline]
ffff8880750fa480 (&ovl_i_mutex_key[depth]){+.+.}-{3:3}, at: ovl_fallocate+0x15c/0x270 fs/overlayfs/file.c:546

but task is already holding lock:
ffff8880750fa480 (&ovl_i_mutex_key[depth]){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:756 [inline]
ffff8880750fa480 (&ovl_i_mutex_key[depth]){+.+.}-{3:3}, at: ovl_fallocate+0x9f/0x270 fs/overlayfs/file.c:535

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


 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syz-executor169/5069:
 #0: ffff88802b1d6460 (sb_writers#9){.+.+}-{0:0}, at: ksys_fallocate fs/open.c:346 [inline]
 #0: ffff88802b1d6460 (sb_writers#9){.+.+}-{0:0}, at: __do_sys_fallocate fs/open.c:354 [inline]
 #0: ffff88802b1d6460 (sb_writers#9){.+.+}-{0:0}, at: __se_sys_fallocate fs/open.c:352 [inline]
 #0: ffff88802b1d6460 (sb_writers#9){.+.+}-{0:0}, at: __x64_sys_fallocate+0xd3/0x140 fs/open.c:352
 #1: ffff8880750fa480 (&ovl_i_mutex_key[depth]){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:756 [inline]
 #1: ffff8880750fa480 (&ovl_i_mutex_key[depth]){+.+.}-{3:3}, at: ovl_fallocate+0x9f/0x270 fs/overlayfs/file.c:535

stack backtrace:
CPU: 1 PID: 5069 Comm: syz-executor169 Not tainted 6.1.0-rc8-next-20221207-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call Trace:
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd1/0x138 lib/dump_stack.c:106
 print_deadlock_bug kernel/locking/lockdep.c:2990 [inline]
 check_deadlock kernel/locking/lockdep.c:3033 [inline]
 validate_chain kernel/locking/lockdep.c:3818 [inline]
 __lock_acquire.cold+0x116/0x3a7 kernel/locking/lockdep.c:5055
 lock_acquire kernel/locking/lockdep.c:5668 [inline]
 lock_acquire+0x1e3/0x630 kernel/locking/lockdep.c:5633
 down_write+0x94/0x220 kernel/locking/rwsem.c:1562
 inode_lock include/linux/fs.h:756 [inline]
 ovl_remove_privs_unlocked fs/overlayfs/file.c:519 [inline]
 ovl_fallocate+0x15c/0x270 fs/overlayfs/file.c:546
 vfs_fallocate+0x48b/0xe00 fs/open.c:323
 ksys_fallocate fs/open.c:346 [inline]
 __do_sys_fallocate fs/open.c:354 [inline]
 __se_sys_fallocate fs/open.c:352 [inline]
 __x64_sys_fallocate+0xd3/0x140 fs/open.c:352
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
RIP: 0033:0x7fa3d1605c29
Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffccc67e118 EFLAGS: 00000246 ORIG_RAX: 000000000000011d
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fa3d1605c29
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007fa3d15c9dd0 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000001000f4 R11: 0000000000000246 R12: 00007fa3d15c9e60
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

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