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Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

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Pull scheduler fix from Thomas Gleixner:
 "A single scheduler fix:

  Prevent idle task from ever being preempted. That makes sure that
  synchronize_rcu_tasks() which is ignoring idle task does not pretend
  that no task is stuck in preempted state. If that happens and idle was
  preempted on a ftrace trampoline the machine crashes due to
  inconsistent state"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/core: Call __schedule() from do_idle() without enabling preemption
This commit is contained in:
Linus Torvalds 2017-05-21 11:52:00 -07:00
commit 970c305aa8
3 changed files with 28 additions and 1 deletions
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25
kernel/sched/core.c
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@ -3502,6 +3502,31 @@ asmlinkage __visible void __sched schedule(void)
}
EXPORT_SYMBOL(schedule);
/*
* synchronize_rcu_tasks() makes sure that no task is stuck in preempted
* state (have scheduled out non-voluntarily) by making sure that all
* tasks have either left the run queue or have gone into user space.
* As idle tasks do not do either, they must not ever be preempted
* (schedule out non-voluntarily).
*
* schedule_idle() is similar to schedule_preempt_disable() except that it
* never enables preemption because it does not call sched_submit_work().
*/
void __sched schedule_idle(void)
{
/*
* As this skips calling sched_submit_work(), which the idle task does
* regardless because that function is a nop when the task is in a
* TASK_RUNNING state, make sure this isn't used someplace that the
* current task can be in any other state. Note, idle is always in the
* TASK_RUNNING state.
*/
WARN_ON_ONCE(current->state);
do {
__schedule(false);
} while (need_resched());
}
#ifdef CONFIG_CONTEXT_TRACKING
asmlinkage __visible void __sched schedule_user(void)
{

2
kernel/sched/idle.c
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@ -265,7 +265,7 @@ static void do_idle(void)
smp_mb__after_atomic();
sched_ttwu_pending();
schedule_preempt_disabled();
schedule_idle();
if (unlikely(klp_patch_pending(current)))
klp_update_patch_state(current);

2
kernel/sched/sched.h
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@ -1467,6 +1467,8 @@ static inline struct cpuidle_state *idle_get_state(struct rq *rq)
}
#endif
extern void schedule_idle(void);
extern void sysrq_sched_debug_show(void);
extern void sched_init_granularity(void);
extern void update_max_interval(void);