quota: check quota reservation on remove_dquot_ref

Reserved space must being claimed before remove_dquot_ref() for a
given inode. Filesystem is responsible for performing force blocks
allocation in case of dealloc in ->quota_off. Let's add sanity check
for that case. Do it similar to add_dquot_ref().

Signed-off-by: Dmitry Monakhov <[e-mail]>
Signed-off-by: Jan Kara <[e-mail]>

fs/quota/dquot.c

···
 		struct list_head *tofree_head)
 {
 	struct inode *inode;
+	int reserved = 0;
 
 	spin_lock(&inode_lock);
 	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
···
 		 *  only quota pointers and these have separate locking
 		 *  (dqptr_sem).
 		 */
-		if (!IS_NOQUOTA(inode))
+		if (!IS_NOQUOTA(inode)) {
+			if (unlikely(inode_get_rsv_space(inode) > 0))
+				reserved = 1;
 			remove_inode_dquot_ref(inode, type, tofree_head);
+		}
 	}
 	spin_unlock(&inode_lock);
+#ifdef CONFIG_QUOTA_DEBUG
+	if (reserved) {
+		printk(KERN_WARNING "VFS (%s): Writes happened after quota"
+			" was disabled thus quota information is probably "
+			"inconsistent. Please run quotacheck(8).\n", sb->s_id);
+	}
+#endif
 }
 
 /* Gather all references from inodes and drop them */