perf_counter: fix uninitialized usage of event_list

Impact: fix boot crash

When doing the generic context switch event I ran into some early
boot hangs, which were caused by inf func recursion (event, fault,
event, fault).

I eventually tracked it down to event_list not being initialized
at the time of the first event. Fix this.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Orig-LKML-Reference: <20090319194233.195392657@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

include/linux/init_task.h

@@ -124,6 +124,8 @@ extern struct cred init_cred;
 # define INIT_PERF_COUNTERS(tsk)					\
 	.perf_counter_ctx.counter_list =				\
 		LIST_HEAD_INIT(tsk.perf_counter_ctx.counter_list),	\
+	.perf_counter_ctx.event_list =					\
+		LIST_HEAD_INIT(tsk.perf_counter_ctx.event_list),	\
 	.perf_counter_ctx.lock =					\
 		__SPIN_LOCK_UNLOCKED(tsk.perf_counter_ctx.lock),
 #else

kernel/perf_counter.c

@@ -1506,7 +1506,7 @@ static void perf_swcounter_ctx_event(struct perf_counter_context *ctx,
 {
 	struct perf_counter *counter;
 
-	if (list_empty(&ctx->event_list))
+	if (system_state != SYSTEM_RUNNING || list_empty(&ctx->event_list))
 		return;
 
 	rcu_read_lock();