4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Frederic Weisbecker <fweisbec@xxxxxxxxx> [ Upstream commit 90d08ba2b9b4be4aeca6a5b5a4b09fbcde30194d ] 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> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/powerpc/kernel/time.c | 1 + 1 file changed, 1 insertion(+) --- a/arch/powerpc/kernel/time.c +++ b/arch/powerpc/kernel/time.c @@ -407,6 +407,7 @@ void arch_vtime_task_switch(struct task_ 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; }