fast_dput(): new rules for refcount

By now there is only one place in entire fast_dput() where we return
false; that happens after refcount had been decremented and found (under
->d_lock) to be zero.  In that case, just prior to returning false to
caller, fast_dput() forcibly changes the refcount from 0 to 1.

Lift that resetting refcount to 1 into the callers; later in the series
it will be massaged out of existence.

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/dcache.c

@@ -847,13 +847,6 @@ locked:
 		spin_unlock(&dentry->d_lock);
 		return true;
 	}
-
-	/*
-	 * Re-get the reference we optimistically dropped. We hold the
-	 * lock, and we just tested that it was zero, so we can just
-	 * set it to 1.
-	 */
-	dentry->d_lockref.count = 1;
 	return false;
 }
 
@@ -896,6 +889,7 @@ void dput(struct dentry *dentry)
 		}
 
 		/* Slow case: now with the dentry lock held */
+		dentry->d_lockref.count = 1;
 		rcu_read_unlock();
 
 		if (likely(retain_dentry(dentry))) {
@@ -930,6 +924,7 @@ void dput_to_list(struct dentry *dentry, struct list_head *list)
 		return;
 	}
 	rcu_read_unlock();
+	dentry->d_lockref.count = 1;
 	if (!retain_dentry(dentry))
 		__dput_to_list(dentry, list);
 	spin_unlock(&dentry->d_lock);