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sched/cgroup: Fix cpu_cgroup_fork() handling

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A new fair task is detached and attached from/to task_group with:

  cgroup_post_fork()
    ss->fork(child) := cpu_cgroup_fork()
      sched_move_task()
        task_move_group_fair()

Which is wrong, because at this point in fork() the task isn't fully
initialized and it cannot 'move' to another group, because its not
attached to any group as yet.

In fact, cpu_cgroup_fork() needs a small part of sched_move_task() so we
can just call this small part directly instead sched_move_task(). And
the task doesn't really migrate because it is not yet attached so we
need the following sequence:

  do_fork()
    sched_fork()
      __set_task_cpu()

    cgroup_post_fork()
      set_task_rq() # set task group and runqueue

    wake_up_new_task()
      select_task_rq() can select a new cpu
      __set_task_cpu
      post_init_entity_util_avg
        attach_task_cfs_rq()
      activate_task
        enqueue_task

This patch makes that happen.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
[ Added TASK_SET_GROUP to set depth properly. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Vincent Guittot
2016-06-17 13:38:55 +02:00
committed by Ingo Molnar
parent 010114739d
commit ea86cb4b76
3 changed files with 67 additions and 24 deletions
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23
kernel/sched/fair.c
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@@ -8466,6 +8466,14 @@ void init_cfs_rq(struct cfs_rq *cfs_rq)
}
#ifdef CONFIG_FAIR_GROUP_SCHED
static void task_set_group_fair(struct task_struct *p)
{
struct sched_entity *se = &p->se;
set_task_rq(p, task_cpu(p));
se->depth = se->parent ? se->parent->depth + 1 : 0;
}
static void task_move_group_fair(struct task_struct *p)
{
detach_task_cfs_rq(p);
@@ -8478,6 +8486,19 @@ static void task_move_group_fair(struct task_struct *p)
attach_task_cfs_rq(p);
}
static void task_change_group_fair(struct task_struct *p, int type)
{
switch (type) {
case TASK_SET_GROUP:
task_set_group_fair(p);
break;
case TASK_MOVE_GROUP:
task_move_group_fair(p);
break;
}
}
void free_fair_sched_group(struct task_group *tg)
{
int i;
@@ -8706,7 +8727,7 @@ const struct sched_class fair_sched_class = {
.update_curr = update_curr_fair,
#ifdef CONFIG_FAIR_GROUP_SCHED
.task_move_group = task_move_group_fair,
.task_change_group = task_change_group_fair,
#endif
};