fs: protect inode->i_state with inode->i_lock

Protect inode state transitions and validity checks with the
inode->i_lock. This enables us to make inode state transitions
independently of the inode_lock and is the first step to peeling
away the inode_lock from the code.

This requires that __iget() is done atomically with i_state checks
during list traversals so that we don't race with another thread
marking the inode I_FREEING between the state check and grabbing the
reference.

Also remove the unlock_new_inode() memory barrier optimisation
required to avoid taking the inode_lock when clearing I_NEW.
Simplify the code by simply taking the inode->i_lock around the
state change and wakeup. Because the wakeup is no longer tricky,
remove the wake_up_inode() function and open code the wakeup where
necessary.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/quotaops.h

@@ -277,7 +277,7 @@ static inline int dquot_alloc_space(struct inode *inode, qsize_t nr)
 		/*
 		 * Mark inode fully dirty. Since we are allocating blocks, inode
 		 * would become fully dirty soon anyway and it reportedly
-		 * reduces inode_lock contention.
+		 * reduces lock contention.
 		 */
 		mark_inode_dirty(inode);
 	}