[BUG] fs: ext4: possible ABBA deadlock in ext4_inline_data_truncate() and ext4_punch_hole()

[Jia-Ju Bai]

Hello,

My static analysis tool reports a possible ABBA deadlock in the ext4 
module in Linux 5.10:

ext4_inline_data_truncate()
  down_write(&EXT4_I(inode)->i_data_sem); --> Line 1895 (Lock A)
  ext4_xattr_ibody_get()
    ext4_xattr_inode_get()
      ext4_xattr_inode_iget()
        inode_lock(inode); --> Line 427 (Lock B)

ext4_punch_hole()
  inode_lock(inode); --> Line 4018 (Lock B)
  ext4_update_disksize_before_punch()
    ext4_update_i_disksize()
      down_write(&EXT4_I(inode)->i_data_sem); --> Line 3248 (Lock A)

When ext4_inline_data_truncate() and ext4_punch_hole() are concurrently 
executed, the deadlock can occur.

I am not quite sure whether this possible deadlock is real and how to 
fix it if it is real.
Any feedback would be appreciated, thanks :)

Reported-by: TOTE Robot <oslab@xxxxxxxxxxxxxxx>


Best wishes,
Jia-Ju Bai