coda_flag_children(): cope with dentries turning negative

->d_lock on parent does not stabilize ->d_inode of child.
We don't do much with that inode in there, but we need
at least to avoid struct inode getting freed under us...

[rcu_read_lock() is not needed here, since parent's ->d_lock
provides an rcu-critical area]
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/coda/cache.c

@@ -94,12 +94,12 @@ static void coda_flag_children(struct dentry *parent, int flag)
 
 	spin_lock(&parent->d_lock);
 	list_for_each_entry(de, &parent->d_subdirs, d_child) {
+		struct inode *inode = d_inode_rcu(de);
 		/* don't know what to do with negative dentries */
-		if (d_inode(de) ) 
-			coda_flag_inode(d_inode(de), flag);
+		if (inode)
+			coda_flag_inode(inode, flag);
 	}
 	spin_unlock(&parent->d_lock);
-	return; 
 }
 
 void coda_flag_inode_children(struct inode *inode, int flag)