Re: [PATCH 04/19] fs: Implement lazy LRU updates for inodes.

Christoph Hellwig
2010-10-17T00:47:13Z

On Sun, Oct 17, 2010 at 04:29:24AM +1100, Nick Piggin wrote:
> > I don't think the pointer check will work either. By the time we retake
> > the lru lock the inode might already have been reaped through a call
> > to invalidate_inodes. There's no way we can do anything with it after
>
> I don't think you're right. If we re take inode_lock, ensure it is on
> the LRU, and call the can_unuse checks, there is no more problem than
> the regular loop taking items from the LRU, AFAIKS.

As long as we have the global inode lock it should indeed be safe.
But once we have a separate lru lock (global or per-zone, with or
without i_lock during the addition) there is nothing preventing the
inode from getting reused and re-added to the lru in the meantime.
Sure this is an extremly unlikely case, but there is no locking to
prevent it once inode_lock is gone.