lift the "already marked killed" case into shrink_dentry_list()

It can happen only when dentry_kill() is called with unlock_on_failure
equal to 0 - other callers had dentry pinned until the moment they've
got ->d_lock and DCACHE_DENTRY_KILLED is set only after lockref_mark_dead().

IOW, only one of three call sites of dentry_kill() might end up reaching
that code.  Just move it there.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/dcache.c

@@ -455,12 +455,6 @@ dentry_kill(struct dentry *dentry, int unlock_on_failure)
 	struct dentry *parent = NULL;
 	bool can_free = true;
 
-	if (unlikely(dentry->d_flags & DCACHE_DENTRY_KILLED)) {
-		can_free = dentry->d_flags & DCACHE_MAY_FREE;
-		spin_unlock(&dentry->d_lock);
-		goto out;
-	}
-
 	inode = dentry->d_inode;
 	if (inode && !spin_trylock(&inode->i_lock)) {
 relock:
@@ -815,6 +809,15 @@ static void shrink_dentry_list(struct list_head *list)
 			continue;
 		}
 
+
+		if (unlikely(dentry->d_flags & DCACHE_DENTRY_KILLED)) {
+			bool can_free = dentry->d_flags & DCACHE_MAY_FREE;
+			spin_unlock(&dentry->d_lock);
+			if (can_free)
+				dentry_free(dentry);
+			continue;
+		}
+
 		parent = dentry_kill(dentry, 0);
 		/*
 		 * If dentry_kill returns NULL, we have nothing more to do.