uprobes: _unregister() should always do register_for_each_vma(false)

uprobe_unregister() removes the breakpoints only if the last consumer
goes away. To support the filtering it should do this every time, we
want to remove the breakpoints which nobody else want to keep.

Note: given that filter_chain() is not actually implemented, this patch
itself doesn't change the behaviour yet, register_for_each_vma(false)
is a heavy "nop" unless there are no more consumers.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

kernel/events/uprobes.c

@@ -825,12 +825,20 @@ static int __uprobe_register(struct uprobe *uprobe)
 	return register_for_each_vma(uprobe, true);
 }
 
-static void __uprobe_unregister(struct uprobe *uprobe)
+static void __uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc)
 {
-	if (!register_for_each_vma(uprobe, false))
-		delete_uprobe(uprobe);
+	int err;
+
+	if (!consumer_del(uprobe, uc))	/* WARN? */
+		return;
 
-	/* TODO : cant unregister? schedule a worker thread */
+	err = register_for_each_vma(uprobe, false);
+	if (!uprobe->consumers) {
+		clear_bit(UPROBE_RUN_HANDLER, &uprobe->flags);
+		/* TODO : cant unregister? schedule a worker thread */
+		if (!err)
+			delete_uprobe(uprobe);
+	}
 }
 
 /*
@@ -868,8 +876,7 @@ int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *
 	} else if (!consumer_add(uprobe, uc)) {
 		ret = __uprobe_register(uprobe);
 		if (ret) {
-			uprobe->consumers = NULL;
-			__uprobe_unregister(uprobe);
+			__uprobe_unregister(uprobe, uc);
 		} else {
 			set_bit(UPROBE_RUN_HANDLER, &uprobe->flags);
 		}
@@ -897,14 +904,7 @@ void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consume
 		return;
 
 	mutex_lock(uprobes_hash(inode));
-
-	if (consumer_del(uprobe, uc)) {
-		if (!uprobe->consumers) {
-			__uprobe_unregister(uprobe);
-			clear_bit(UPROBE_RUN_HANDLER, &uprobe->flags);
-		}
-	}
-
+	__uprobe_unregister(uprobe, uc);
 	mutex_unlock(uprobes_hash(inode));
 	put_uprobe(uprobe);
 }