sched: Remove the obsolete exit_state/signal hacks

account_group_xxx() functions check ->exit_state to ensure that
current->signal is valid and can't go away. This is not needed
since ea6d290c, task->signal is pinned to task_struct.

The comment and another hack in account_group_exec_runtime() refers
to task_rq_unlock_wait() which was already removed by b7b8ff63.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100610230952.GA25914@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched_stats.h

@@ -295,13 +295,7 @@ sched_info_switch(struct task_struct *prev, struct task_struct *next)
 static inline void account_group_user_time(struct task_struct *tsk,
 					   cputime_t cputime)
 {
-	struct thread_group_cputimer *cputimer;
-
-	/* tsk == current, ensure it is safe to use ->signal */
-	if (unlikely(tsk->exit_state))
-		return;
-
-	cputimer = &tsk->signal->cputimer;
+	struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
 
 	if (!cputimer->running)
 		return;
@@ -325,13 +319,7 @@ static inline void account_group_user_time(struct task_struct *tsk,
 static inline void account_group_system_time(struct task_struct *tsk,
 					     cputime_t cputime)
 {
-	struct thread_group_cputimer *cputimer;
-
-	/* tsk == current, ensure it is safe to use ->signal */
-	if (unlikely(tsk->exit_state))
-		return;
-
-	cputimer = &tsk->signal->cputimer;
+	struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
 
 	if (!cputimer->running)
 		return;
@@ -355,16 +343,7 @@ static inline void account_group_system_time(struct task_struct *tsk,
 static inline void account_group_exec_runtime(struct task_struct *tsk,
 					      unsigned long long ns)
 {
-	struct thread_group_cputimer *cputimer;
-	struct signal_struct *sig;
-
-	sig = tsk->signal;
-	/* see __exit_signal()->task_rq_unlock_wait() */
-	barrier();
-	if (unlikely(!sig))
-		return;
-
-	cputimer = &sig->cputimer;
+	struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
 
 	if (!cputimer->running)
 		return;