[BUG REPORT] potential deadlock in inode evicting under the inode lru traversing context on ext4 and ubifs

[Ryder Wang]

> Um, I don't see how this can happen.  If the ea_inode is in use,
> i_count will be greater than zero, and hence the inode will never be
> go down the rest of the path in inode_lru_inode():
> 
>         if (atomic_read(&inode->i_count) ||
>             ...) {
>                 list_lru_isolate(lru, &inode->i_lru);
>                 spin_unlock(&inode->i_lock);
>                 this_cpu_dec(nr_unused);
>                 return LRU_REMOVED;
>         }

Yes, in the function inode_lru_inode (in case of clearing cache), there has been such inode->i_state check mechanism to avoid double-removing the inode which is being removed by another process. Unluckily, no such similar inode->i_state check mechanism in the function iput_final (in case of removing file), so double-removing inode can still appear.

It looks we need to add some inode->i_state check in iput_final() , if we want to fix this race condition bug.