uprobes: Kill UPROBE_RUN_HANDLER flag

Simply remove UPROBE_RUN_HANDLER and the corresponding code.

It can only help if uprobe has a single consumer, and in fact
it is no longer needed after handler_chain() was changed to use
->register_rwsem, we simply can not race with uprobe_register().
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

kernel/events/uprobes.c

@@ -83,10 +83,8 @@ static atomic_t uprobe_events = ATOMIC_INIT(0);
 
 /* Have a copy of original instruction */
 #define UPROBE_COPY_INSN	0
-/* Dont run handlers when first register/ last unregister in progress*/
-#define UPROBE_RUN_HANDLER	1
 /* Can skip singlestep */
-#define UPROBE_SKIP_SSTEP	2
+#define UPROBE_SKIP_SSTEP	1
 
 struct uprobe {
 	struct rb_node		rb_node;	/* node in the rb tree */
@@ -475,9 +473,6 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
 {
 	struct uprobe_consumer *uc;
 
-	if (!test_bit(UPROBE_RUN_HANDLER, &uprobe->flags))
-		return;
-
 	down_read(&uprobe->register_rwsem);
 	for (uc = uprobe->consumers; uc; uc = uc->next)
 		uc->handler(uc, regs);
@@ -825,13 +820,8 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
 
 static int __uprobe_register(struct uprobe *uprobe, struct uprobe_consumer *uc)
 {
-	int err;
-
 	consumer_add(uprobe, uc);
-	err = register_for_each_vma(uprobe, true);
-	if (!err) /* TODO: pointless unless the first consumer */
-		set_bit(UPROBE_RUN_HANDLER, &uprobe->flags);
-	return err;
+	return register_for_each_vma(uprobe, true);
 }
 
 static void __uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc)
@@ -842,12 +832,9 @@ static void __uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *u
 		return;
 
 	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)
+	if (!uprobe->consumers && !err)
 		delete_uprobe(uprobe);
-	}
 }
 
 /*