[tip:sched/core] sched/cputime, ia64: Fix incorrect start cputime assignment on task switch

[tip-bot for Frederic Weisbecker]

Commit-ID:  8388d21468e7e7656867b67ab2ec98a78c9ad799
Gitweb:     http://git.kernel.org/tip/8388d21468e7e7656867b67ab2ec98a78c9ad799
Author:     Frederic Weisbecker <fweisbec@xxxxxxxxx>
AuthorDate: Thu, 5 Jan 2017 18:11:42 +0100
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Sat, 14 Jan 2017 09:54:11 +0100

sched/cputime, ia64: Fix incorrect start cputime assignment on task switch

On task switch we must initialize the current cputime of the next task
using the value of the previous task which got freshly updated.

But we are confusing that with doing the opposite, which should result
in incorrect cputime accounting.

Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1483636310-6557-3-git-send-email-fweisbec@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/ia64/kernel/time.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/ia64/kernel/time.c b/arch/ia64/kernel/time.c
index 71775b95..637e741 100644
--- a/arch/ia64/kernel/time.c
+++ b/arch/ia64/kernel/time.c
@@ -83,7 +83,7 @@ void arch_vtime_task_switch(struct task_struct *prev)
 	struct thread_info *pi = task_thread_info(prev);
 	struct thread_info *ni = task_thread_info(current);
 
-	pi->ac_stamp = ni->ac_stamp;
+	ni->ac_stamp = pi->ac_stamp;
 	ni->ac_stime = ni->ac_utime = 0;
 }