On Sat, Oct 16, 2010 at 08:47:10PM -0400, Christoph Hellwig wrote: > 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. No. There is nothing preventing that exact reuse from happening in mainline _today_ either, because the inode_lock is dropped there too. The point is that it is a heuristic that works (apparently) most of the time but if it gets it wrong then it's not a big deal, it's only the LRU position anyway. It would work exactly the same with separate global or per-zone lru locks. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
