[tip:sched/core] sched/cputime, powerpc32: Fix stale scaled stime on context switch

[tip-bot for Frederic Weisbecker]

Commit-ID:  90d08ba2b9b4be4aeca6a5b5a4b09fbcde30194d
Gitweb:     http://git.kernel.org/tip/90d08ba2b9b4be4aeca6a5b5a4b09fbcde30194d
Author:     Frederic Weisbecker <fweisbec@xxxxxxxxx>
AuthorDate: Thu, 5 Jan 2017 18:11:41 +0100
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Sat, 14 Jan 2017 09:54:11 +0100

sched/cputime, powerpc32: Fix stale scaled stime on context switch

On context switch with powerpc32, the cputime is accumulated in the
thread_info struct. So the switching-in task must move forward its
start time snapshot to the current time in order to later compute the
delta spent in system mode.

This is what we do for the normal cputime by initializing the starttime
field to the value of the previous task's starttime which got freshly
updated.

But we are missing the update of the scaled cputime start time. As a
result we may be accounting too much scaled cputime later.

Fix this by initializing the scaled cputime the same way we do for
normal cputime.

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/1483636310-6557-2-git-send-email-fweisbec@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/powerpc/kernel/time.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index bc2e08d..ce21650 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -407,6 +407,7 @@ void arch_vtime_task_switch(struct task_struct *prev)
 	struct cpu_accounting_data *acct = get_accounting(current);
 
 	acct->starttime = get_accounting(prev)->starttime;
+	acct->startspurr = get_accounting(prev)->startspurr;
 	acct->system_time = 0;
 	acct->user_time = 0;
 }