syzbot

bcachefs (loop3): reading snapshots table
bcachefs (loop3): reading snapshots done
bcachefs (loop3): done starting filesystem
============================================
WARNING: possible recursive locking detected
6.14.0-syzkaller-10892-g4e82c87058f4 #0 Not tainted
--------------------------------------------
syz.3.14/5986 is trying to acquire lock:
ffff88805a8abe08 (&sb->s_type->i_mutex_key#26){++++}-{4:4}, at: inode_lock include/linux/fs.h:867 [inline]
ffff88805a8abe08 (&sb->s_type->i_mutex_key#26){++++}-{4:4}, at: bch2_symlink+0x178/0x320 fs/bcachefs/fs.c:858

but task is already holding lock:
ffff88805a8ab670 (&sb->s_type->i_mutex_key#26){++++}-{4:4}, at: inode_lock include/linux/fs.h:867 [inline]
ffff88805a8ab670 (&sb->s_type->i_mutex_key#26){++++}-{4:4}, at: ovl_copy_up_workdir fs/overlayfs/copy_up.c:782 [inline]
ffff88805a8ab670 (&sb->s_type->i_mutex_key#26){++++}-{4:4}, at: ovl_do_copy_up fs/overlayfs/copy_up.c:1001 [inline]
ffff88805a8ab670 (&sb->s_type->i_mutex_key#26){++++}-{4:4}, at: ovl_copy_up_one fs/overlayfs/copy_up.c:1202 [inline]
ffff88805a8ab670 (&sb->s_type->i_mutex_key#26){++++}-{4:4}, at: ovl_copy_up_flags+0x19d7/0x47f0 fs/overlayfs/copy_up.c:1257

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

       CPU0
       ----
  lock(&sb->s_type->i_mutex_key#26);
  lock(&sb->s_type->i_mutex_key#26);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

6 locks held by syz.3.14/5986:
 #0: ffff888025bd2420 (sb_writers#18){.+.+}-{0:0}, at: mnt_want_write+0x3f/0x90 fs/namespace.c:556
 #1: ffff888078339e50 (&ovl_i_mutex_dir_key[depth]/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:902 [inline]
 #1: ffff888078339e50 (&ovl_i_mutex_dir_key[depth]/1){+.+.}-{4:4}, at: do_unlinkat+0x26c/0x7b0 fs/namei.c:4595
 #2: ffff88807833a418 (&ovl_i_mutex_key[depth]){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:867 [inline]
 #2: ffff88807833a418 (&ovl_i_mutex_key[depth]){+.+.}-{4:4}, at: vfs_unlink+0xe4/0x650 fs/namei.c:4533
 #3: ffff88807833a7d0 (&ovl_i_lock_key[depth]){+.+.}-{4:4}, at: ovl_inode_lock_interruptible fs/overlayfs/overlayfs.h:651 [inline]
 #3: ffff88807833a7d0 (&ovl_i_lock_key[depth]){+.+.}-{4:4}, at: ovl_copy_up_start+0x53/0x310 fs/overlayfs/util.c:727
 #4: ffff888054182420 (sb_writers#17){.+.+}-{0:0}, at: ovl_copy_up_workdir fs/overlayfs/copy_up.c:781 [inline]
 #4: ffff888054182420 (sb_writers#17){.+.+}-{0:0}, at: ovl_do_copy_up fs/overlayfs/copy_up.c:1001 [inline]
 #4: ffff888054182420 (sb_writers#17){.+.+}-{0:0}, at: ovl_copy_up_one fs/overlayfs/copy_up.c:1202 [inline]
 #4: ffff888054182420 (sb_writers#17){.+.+}-{0:0}, at: ovl_copy_up_flags+0x19c0/0x47f0 fs/overlayfs/copy_up.c:1257
 #5: ffff88805a8ab670 (&sb->s_type->i_mutex_key#26){++++}-{4:4}, at: inode_lock include/linux/fs.h:867 [inline]
 #5: ffff88805a8ab670 (&sb->s_type->i_mutex_key#26){++++}-{4:4}, at: ovl_copy_up_workdir fs/overlayfs/copy_up.c:782 [inline]
 #5: ffff88805a8ab670 (&sb->s_type->i_mutex_key#26){++++}-{4:4}, at: ovl_do_copy_up fs/overlayfs/copy_up.c:1001 [inline]
 #5: ffff88805a8ab670 (&sb->s_type->i_mutex_key#26){++++}-{4:4}, at: ovl_copy_up_one fs/overlayfs/copy_up.c:1202 [inline]
 #5: ffff88805a8ab670 (&sb->s_type->i_mutex_key#26){++++}-{4:4}, at: ovl_copy_up_flags+0x19d7/0x47f0 fs/overlayfs/copy_up.c:1257

stack backtrace:
CPU: 1 UID: 0 PID: 5986 Comm: syz.3.14 Not tainted 6.14.0-syzkaller-10892-g4e82c87058f4 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_deadlock_bug+0x2be/0x2d0 kernel/locking/lockdep.c:3042
 check_deadlock kernel/locking/lockdep.c:3094 [inline]
 validate_chain+0x928/0x24e0 kernel/locking/lockdep.c:3896
 __lock_acquire+0xad5/0xd80 kernel/locking/lockdep.c:5235
 lock_acquire+0x116/0x2f0 kernel/locking/lockdep.c:5866
 down_write+0x9c/0x220 kernel/locking/rwsem.c:1577
 inode_lock include/linux/fs.h:867 [inline]
 bch2_symlink+0x178/0x320 fs/bcachefs/fs.c:858
 vfs_symlink+0x137/0x2e0 fs/namei.c:4688
 ovl_do_symlink+0x85/0xd0 fs/overlayfs/overlayfs.h:268
 ovl_create_real+0x271/0x460 fs/overlayfs/dir.c:176
 ovl_copy_up_workdir fs/overlayfs/copy_up.c:783 [inline]
 ovl_do_copy_up fs/overlayfs/copy_up.c:1001 [inline]
 ovl_copy_up_one fs/overlayfs/copy_up.c:1202 [inline]
 ovl_copy_up_flags+0x1a0a/0x47f0 fs/overlayfs/copy_up.c:1257
 ovl_nlink_start+0x9c/0x410 fs/overlayfs/util.c:1165
 ovl_do_remove+0x242/0xda0 fs/overlayfs/dir.c:892
 vfs_unlink+0x365/0x650 fs/namei.c:4544
 do_unlinkat+0x442/0x7b0 fs/namei.c:4608
 __do_sys_unlink fs/namei.c:4654 [inline]
 __se_sys_unlink fs/namei.c:4652 [inline]
 __x64_sys_unlink+0x47/0x50 fs/namei.c:4652
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc4ad18d169
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fc4adf6f038 EFLAGS: 00000246 ORIG_RAX: 0000000000000057
RAX: ffffffffffffffda RBX: 00007fc4ad3a5fa0 RCX: 00007fc4ad18d169
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000200000000440
RBP: 00007fc4ad20e2a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fc4ad3a5fa0 R15: 00007ffc7a88c648
 </TASK>
bcachefs (loop3): shutting down
bcachefs (loop3): going read-only
bcachefs (loop3): finished waiting for writes to stop
bcachefs (loop3): flushing journal and stopping allocators, journal seq 5
bcachefs (loop3): flushing journal and stopping allocators complete, journal seq 5
bcachefs (loop3): clean shutdown complete, journal seq 6
bcachefs (loop3): marking filesystem clean
bcachefs (loop3): shutdown complete
syz.3.14 (5986) used greatest stack depth: 12208 bytes left