[patch] sched/autogroup: Fix 64bit kernel nice adjustment

[Mike Galbraith]

On Tue, 2016-11-22 at 16:59 +0100, Michael Kerrisk (man-pages) wrote:

>        ┌─────────────────────────────────────────────────────┐
>        │FIXME                                                │
>        ├─────────────────────────────────────────────────────┤
>        │Regarding the previous paragraph...  My tests  indi‐ │
>        │cate  that writing *any* value to the autogroup file │
>        │causes the task group to get a lower priority.  This │

Because autogroup didn't call the then meaningless scale_load()...


Autogroup nice level adjustment has been broken ever since load
resolution was increased for 64bit kernels.  Use scale_load() to
scale group weight.

Signed-off-by: Mike Galbraith <umgwanakikb...@gmail.com>
Reported-by: Michael Kerrisk <mtk.manpa...@gmail.com>
Cc: sta...@vger.kernel.org
---
 kernel/sched/auto_group.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/sched/auto_group.c
+++ b/kernel/sched/auto_group.c
@@ -192,6 +192,7 @@ int proc_sched_autogroup_set_nice(struct
 {
        static unsigned long next = INITIAL_JIFFIES;
        struct autogroup *ag;
+       unsigned long shares;
        int err;
 
        if (nice < MIN_NICE || nice > MAX_NICE)
@@ -210,9 +211,10 @@ int proc_sched_autogroup_set_nice(struct
 
        next = HZ / 10 + jiffies;
        ag = autogroup_task_get(p);
+       shares = scale_load(sched_prio_to_weight[nice + 20]);
 
        down_write(&ag->lock);
-       err = sched_group_set_shares(ag->tg, sched_prio_to_weight[nice + 20]);
+       err = sched_group_set_shares(ag->tg, shares);
        if (!err)
                ag->nice = nice;
        up_write(&ag->lock);