Commit b23decf8 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Peter Zijlstra
Browse files

sched: Initialize idle tasks only once 



Idle tasks are initialized via __sched_fork() twice:

     fork_idle()
        copy_process()
	  sched_fork()
             __sched_fork()
	init_idle()
          __sched_fork()

Instead of cleaning this up, sched_ext hacked around it. Even when analyis
and solution were provided in a discussion, nobody cared to clean this up.

init_idle() is also invoked from sched_init() to initialize the boot CPU's
idle task, which requires the __sched_fork() invocation. But this can be
trivially solved by invoking __sched_fork() before init_idle() in
sched_init() and removing the __sched_fork() invocation from init_idle().

Do so and clean up the comments explaining this historical leftover.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20241028103142.359584747@linutronix.de
parent 1a615101

kernel/sched/core.c

+5 −7
Original line number Diff line number Diff line
@@ -4423,7 +4423,8 @@ int wake_up_state(struct task_struct *p, unsigned int state) 
 * Perform scheduler related setup for a newly forked process p.

 * p is forked by current.

 *

 * __sched_fork() is basic setup used by init_idle() too:

 * __sched_fork() is basic setup which is also used by sched_init() to

 * initialize the boot CPU's idle task.

 */

static void __sched_fork(unsigned long clone_flags, struct task_struct *p)

{
@@ -7697,8 +7698,6 @@ void __init init_idle(struct task_struct *idle, int cpu) 
	struct rq *rq = cpu_rq(cpu);

	unsigned long flags;



	__sched_fork(0, idle);



	raw_spin_lock_irqsave(&idle->pi_lock, flags);

	raw_spin_rq_lock(rq);
@@ -7713,10 +7712,8 @@ void __init init_idle(struct task_struct *idle, int cpu) 


#ifdef CONFIG_SMP

	/*

	 * It's possible that init_idle() gets called multiple times on a task,

	 * in that case do_set_cpus_allowed() will not do the right thing.

	 *

	 * And since this is boot we can forgo the serialization.

	 * No validation and serialization required at boot time and for

	 * setting up the idle tasks of not yet online CPUs.

	 */

	set_cpus_allowed_common(idle, &ac);

#endif
@@ -8561,6 +8558,7 @@ void __init sched_init(void) 
	 * but because we are the idle thread, we just pick up running again

	 * when this runqueue becomes "idle".

	 */

	__sched_fork(0, current);

	init_idle(current, smp_processor_id());



	calc_load_update = jiffies + LOAD_FREQ;