• Filipe Manana's avatar
    Btrfs: fix deadlock between clone/dedupe and rename · 4ea748e1
    Filipe Manana authored
    Reflinking (clone/dedupe) and rename are operations that operate on two
    inodes and therefore need to lock them in the same order to avoid ABBA
    deadlocks. It happens that Btrfs' reflink implementation always locked
    them in a different order from VFS's lock_two_nondirectories() helper,
    which is used by the rename code in VFS, resulting in ABBA type deadlocks.
    
    Btrfs' locking order:
    
      static void btrfs_double_inode_lock(struct inode *inode1, struct inode *inode2)
      {
             if (inode1 < inode2)
                    swap(inode1, inode2);
    
             inode_lock_nested(inode1, I_MUTEX_PARENT);
             inode_lock_nested(inode2, I_MUTEX_CHILD);
      }
    
    VFS's locking order:
    
      void lock_two_nondirectories(struct inode *inode1, struct inode *inode2)
      {
            if (inode1 > inode2)
                    swap(inode1, inode2);
    
            if (inode1 && !S_ISDIR(inode1->i_mode))
                    inode_lock(inode1);
            if (inode2 && !S_ISDIR(inode2->i_mode) && inode2 != inode1)
                    inode_lock_nested(inode2, I_MUTEX_NONDIR2);
    }
    
    Fix this by killing the btrfs helper function that does the double inode
    locking and replace it with VFS's helper lock_two_nondirectories().
    Reported-by: default avatarZygo Blaxell <ce3g8jdj@umail.furryterror.org>
    Fixes: 416161db ("btrfs: offline dedupe")
    CC: stable@vger.kernel.org # 4.4+
    Signed-off-by: default avatarFilipe Manana <fdmanana@suse.com>
    Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
    4ea748e1
ioctl.c 139 KB