6.6-stable review patch. If anyone has any objections, please let me know.
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From: Thomas Gleixner tglx@linutronix.de
[ Upstream commit b23decf8ac9102fc52c4de5196f4dc0a5f3eb80b ]
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: Thomas Gleixner tglx@linutronix.de Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lore.kernel.org/r/20241028103142.359584747@linutronix.de Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/core.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 228f7c07da72..86606fb9e6bc 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4488,7 +4488,8 @@ 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) { @@ -9257,8 +9258,6 @@ 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);
@@ -9273,10 +9272,8 @@ 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 @@ -10105,6 +10102,7 @@ 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;