Patch "sched/cputime, powerpc32: Fix stale scaled stime on context switch" has been added to the 4.9-stable tree

Patch "sched/cputime, powerpc32: Fix stale scaled stime on context switch" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

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

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     sched-cputime-powerpc32-fix-stale-scaled-stime-on-context-switch.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Thu Nov  9 09:48:01 CET 2017
From: Frederic Weisbecker <fweisbec@gmail.com>
Date: Thu, 5 Jan 2017 18:11:41 +0100
Subject: sched/cputime, powerpc32: Fix stale scaled stime on context switch

From: Frederic Weisbecker <fweisbec@gmail.com>


[ 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@gmail.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Wanpeng Li <wanpeng.li@hotmail.com>
Link: http://lkml.kernel.org/r/1483636310-6557-2-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 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;
 }


Patches currently in stable-queue which might be from fweisbec@gmail.com are

queue-4.9/sched-cputime-powerpc32-fix-stale-scaled-stime-on-context-switch.patch