[PATCH] fix nr_unused accounting, and avoid recursing in iput with I_WILL_FREE set

 			list_move(&inode->i_list, &inode_in_use);
 		} else {
 			list_move(&inode->i_list, &inode_unused);
+			inodes_stat.nr_unused++;
 		}
 	}
 	wake_up_inode(inode);

Are you sure the above diff is correct? It was added somewhere between
2.6.5 and 2.6.8. I think it's wrong.

The only way I can imagine the i_count to be zero in the above path, is
that I_WILL_FREE is set.  And if I_WILL_FREE is set, then we must not
increase nr_unused.  So I believe the above change is buggy and it will
definitely overstate the number of unused inodes and it should be backed
out.

Note that __writeback_single_inode before calling __sync_single_inode, can
drop the spinlock and we can have both the dirty and locked bitflags clear
here:

		spin_unlock(&inode_lock);
		__wait_on_inode(inode);
		iput(inode);
XXXXXXX
		spin_lock(&inode_lock);
	}
	use inode again here

a construct like the above makes zero sense from a reference counting
standpoint.
...