hw-breakpoints: Use overflow handler instead of the event callback

struct perf_event::event callback was called when a breakpoint
triggers. But this is a rather opaque callback, pretty
tied-only to the breakpoint API and not really integrated into perf
as it triggers even when we don't overflow.

We prefer to use overflow_handler() as it fits into the perf events
rules, being called only when we overflow.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: "K. Prasad" <prasad@linux.vnet.ibm.com>
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 84bd28a..d2f2667 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -565,10 +565,13 @@
 	void (*func)(struct perf_pending_entry *);
 };
 
-typedef void (*perf_callback_t)(struct perf_event *, void *);
-
 struct perf_sample_data;
 
+typedef void (*perf_callback_t)(struct perf_event *, void *);
+typedef void (*perf_overflow_handler_t)(struct perf_event *, int,
+					struct perf_sample_data *,
+					struct pt_regs *regs);
+
 /**
  * struct perf_event - performance event kernel representation:
  */
@@ -660,9 +663,7 @@
 	struct pid_namespace		*ns;
 	u64				id;
 
-	void (*overflow_handler)(struct perf_event *event,
-			int nmi, struct perf_sample_data *data,
-			struct pt_regs *regs);
+	perf_overflow_handler_t		overflow_handler;
 
 #ifdef CONFIG_EVENT_PROFILE
 	struct event_filter		*filter;
@@ -779,7 +780,7 @@
 perf_event_create_kernel_counter(struct perf_event_attr *attr,
 				int cpu,
 				pid_t pid,
-				perf_callback_t callback);
+				perf_overflow_handler_t callback);
 extern u64 perf_event_read_value(struct perf_event *event,
 				 u64 *enabled, u64 *running);