• Tahsin Erdogan's avatar
    ext4: fix lockdep warning about recursive inode locking · 33d201e0
    Tahsin Erdogan authored
    Setting a large xattr value may require writing the attribute contents
    to an external inode. In this case we may need to lock the xattr inode
    along with the parent inode. This doesn't pose a deadlock risk because
    xattr inodes are not directly visible to the user and their access is
    restricted.
    
    Assign a lockdep subclass to xattr inode's lock.
    
     ============================================
     WARNING: possible recursive locking detected
     4.12.0-rc1+ #740 Not tainted
     --------------------------------------------
     python/1822 is trying to acquire lock:
      (&sb->s_type->i_mutex_key#15){+.+...}, at: [<ffffffff804912ca>] ext4_xattr_set_entry+0x65a/0x7b0
    
     but task is already holding lock:
      (&sb->s_type->i_mutex_key#15){+.+...}, at: [<ffffffff803d6687>] vfs_setxattr+0x57/0xb0
    
     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
    
     4 locks held by python/1822:
      #0:  (sb_writers#10){.+.+.+}, at: [<ffffffff803d0eef>] mnt_want_write+0x1f/0x50
      #1:  (&sb->s_type->i_mutex_key#15){+.+...}, at: [<ffffffff803d6687>] vfs_setxattr+0x57/0xb0
      #2:  (jbd2_handle){.+.+..}, at: [<ffffffff80493f40>] start_this_handle+0xf0/0x420
      #3:  (&ei->xattr_sem){++++..}, at: [<ffffffff804920ba>] ext4_xattr_set_handle+0x9a/0x4f0
    
     stack backtrace:
     CPU: 0 PID: 1822 Comm: python Not tainted 4.12.0-rc1+ #740
     Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
     Call Trace:
      dump_stack+0x67/0x9e
      __lock_acquire+0x5f3/0x1750
      lock_acquire+0xb5/0x1d0
      down_write+0x2c/0x60
      ext4_xattr_set_entry+0x65a/0x7b0
      ext4_xattr_block_set+0x1b2/0x9b0
      ext4_xattr_set_handle+0x322/0x4f0
      ext4_xattr_set+0x144/0x1a0
      ext4_xattr_user_set+0x34/0x40
      __vfs_setxattr+0x66/0x80
      __vfs_setxattr_noperm+0x69/0x1c0
      vfs_setxattr+0xa2/0xb0
      setxattr+0x12e/0x150
      path_setxattr+0x87/0xb0
      SyS_setxattr+0xf/0x20
      entry_SYSCALL_64_fastpath+0x18/0xad
    Signed-off-by: default avatarTahsin Erdogan <tahsin@google.com>
    Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
    33d201e0
xattr.h 6.81 KB