[syzbot] [fs?] possible deadlock in __simple_recursive_removal

[syzbot <syzbot+6d7771315ecb9233f395@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    50c8770a42fa Add linux-next specific files for 20250702
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=152d348c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=70c16e4e191115d4
dashboard link: https://syzkaller.appspot.com/bug?extid=6d7771315ecb9233f395
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=106bd770580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=164b048c580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3d4ef6bedc5b/disk-50c8770a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/15b7565dc0ef/vmlinux-50c8770a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3b397342a62b/bzImage-50c8770a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6d7771315ecb9233f395@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
6.16.0-rc4-next-20250702-syzkaller #0 Not tainted
--------------------------------------------
syz-executor365/5837 is trying to acquire lock:
ffff8880792cc650 (&sb->s_type->i_mutex_key#15){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:869 [inline]
ffff8880792cc650 (&sb->s_type->i_mutex_key#15){+.+.}-{4:4}, at: __simple_recursive_removal+0x95/0x510 fs/libfs.c:614

but task is already holding lock:
ffff888027bf0148 (&sb->s_type->i_mutex_key#15){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:869 [inline]
ffff888027bf0148 (&sb->s_type->i_mutex_key#15){+.+.}-{4:4}, at: bm_entry_write+0x289/0x540 fs/binfmt_misc.c:737

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

       CPU0
       ----
  lock(&sb->s_type->i_mutex_key#15);
  lock(&sb->s_type->i_mutex_key#15);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syz-executor365/5837:
 #0: ffff88807e5fc428 (sb_writers#8){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:3098 [inline]
 #0: ffff88807e5fc428 (sb_writers#8){.+.+}-{0:0}, at: vfs_write+0x211/0xa90 fs/read_write.c:682
 #1: ffff888027bf0148 (&sb->s_type->i_mutex_key#15){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:869 [inline]
 #1: ffff888027bf0148 (&sb->s_type->i_mutex_key#15){+.+.}-{4:4}, at: bm_entry_write+0x289/0x540 fs/binfmt_misc.c:737

stack backtrace:
CPU: 0 UID: 0 PID: 5837 Comm: syz-executor365 Not tainted 6.16.0-rc4-next-20250702-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_deadlock_bug+0x28b/0x2a0 kernel/locking/lockdep.c:3044
 check_deadlock kernel/locking/lockdep.c:3096 [inline]
 validate_chain+0x1a3f/0x2140 kernel/locking/lockdep.c:3898
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
 down_write+0x96/0x1f0 kernel/locking/rwsem.c:1577
 inode_lock include/linux/fs.h:869 [inline]
 __simple_recursive_removal+0x95/0x510 fs/libfs.c:614
 remove_binfmt_handler fs/binfmt_misc.c:694 [inline]
 bm_entry_write+0x4f7/0x540 fs/binfmt_misc.c:749
 vfs_write+0x27e/0xa90 fs/read_write.c:684
 ksys_write+0x145/0x250 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f147e7aa369
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 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:00007ffed0db9fa8 EFLAGS: 00000246 ORIG_RAX


---
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