[PATCH] s390: cputime misaccounting

finish_arch_switch needs to update the user cpu time as well, not just the
system cpu time. Otherwise the partial user cpu time of a process that is
stored in the lowcore will be (mis-)accounted to the next process.

Signed-off-by: Martin Schwidefsky <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/s390/kernel/time.c

···
 #endif
 
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
-	account_user_vtime(current);
+	account_tick_vtime(current);
 #else
 	while (ticks--)
 		update_process_times(user_mode(regs));

arch/s390/kernel/vtime.c

···
  * Update process times based on virtual cpu times stored by entry.S
  * to the lowcore fields user_timer, system_timer & steal_clock.
  */
-void account_user_vtime(struct task_struct *tsk)
+void account_tick_vtime(struct task_struct *tsk)
 {
 	cputime_t cputime;
 	__u64 timer, clock;
···
 		rcu_check_callbacks(smp_processor_id(), rcu_user_flag);
 	scheduler_tick();
  	run_posix_cpu_timers(tsk);
+}
+
+/*
+ * Update process times based on virtual cpu times stored by entry.S
+ * to the lowcore fields user_timer, system_timer & steal_clock.
+ */
+void account_vtime(struct task_struct *tsk)
+{
+	cputime_t cputime;
+	__u64 timer;
+
+	timer = S390_lowcore.last_update_timer;
+	asm volatile ("  STPT %0"    /* Store current cpu timer value */
+		      : "=m" (S390_lowcore.last_update_timer) );
+	S390_lowcore.system_timer += timer - S390_lowcore.last_update_timer;
+
+	cputime = S390_lowcore.user_timer >> 12;
+	S390_lowcore.user_timer -= cputime << 12;
+	S390_lowcore.steal_clock -= cputime << 12;
+	account_user_time(tsk, cputime);
+
+	cputime =  S390_lowcore.system_timer >> 12;
+	S390_lowcore.system_timer -= cputime << 12;
+	S390_lowcore.steal_clock -= cputime << 12;
+	account_system_time(tsk, 0, cputime);
 }
 
 /*

include/asm-s390/system.h

···
 }
 
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
-extern void account_user_vtime(struct task_struct *);
+extern void account_vtime(struct task_struct *);
+extern void account_tick_vtime(struct task_struct *);
 extern void account_system_vtime(struct task_struct *);
 #endif
 
 #define finish_arch_switch(prev) do {					     \
 	set_fs(current->thread.mm_segment);				     \
-	account_system_vtime(prev);					     \
+	account_vtime(prev);						     \
 } while (0)
 
 #define nop() __asm__ __volatile__ ("nop")

include/linux/hardirq.h

···
 struct task_struct;
 
 #ifndef CONFIG_VIRT_CPU_ACCOUNTING
-static inline void account_user_vtime(struct task_struct *tsk)
-{
-}
-
 static inline void account_system_vtime(struct task_struct *tsk)
 {
 }