sched: Fix the PREEMPT_ACTIVE check in __trace_sched_switch_state()

task_preempt_count() has nothing to do with the actual preempt counter,
thread_info->saved_preempt_count is only valid right after switch_to().

__trace_sched_switch_state() can use preempt_count(), prev is still the
current task when trace_sched_switch() is called.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
[ Added BUG_ON(). ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20141007195108.GB28002@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 6 insertions, 3 deletions

diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 0a68d5ae584e..30fedaf3e56a 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -97,16 +97,19 @@ static inline long __trace_sched_switch_state(struct task_struct *p)
         long state = p->state;
 
 #ifdef CONFIG_PREEMPT
+#ifdef CONFIG_SCHED_DEBUG
+        BUG_ON(p != current);
+#endif /* CONFIG_SCHED_DEBUG */
         /*
          * For all intents and purposes a preempted task is a running task.
          */
-        if (task_preempt_count(p) & PREEMPT_ACTIVE)
+        if (preempt_count() & PREEMPT_ACTIVE)
                 state = TASK_RUNNING | TASK_STATE_MAX;
-#endif
+#endif /* CONFIG_PREEMPT */
 
         return state;
 }
-#endif
+#endif /* CREATE_TRACE_POINTS */
 
 /*
  * Tracepoint for task switches, performed by the scheduler: