From af0fffd9300b97d8875aa745bc78e2f6fdb3c1f0 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Fri, 6 Jul 2018 15:06:15 +0200 Subject: sched/core: Remove get_cpu() from sched_fork() get_cpu() disables preemption for the entire sched_fork() function. This get_cpu() was introduced in commit: dd41f596cda0 ("sched: cfs core code") ... which also invoked sched_balance_self() and this function required preemption do be off. Today, sched_balance_self() seems to be moved to ->task_fork callback which is invoked while the ->pi_lock is held. set_load_weight() could invoke reweight_task() which then via $callchain might end up in smp_processor_id() but since `update_load' is false this won't happen. I didn't find any this_cpu*() or similar usage during the initialisation of the task_struct. The `cpu' value (from get_cpu()) is only used later in __set_task_cpu() while the ->pi_lock lock is held. Based on this it is possible to remove get_cpu() and use smp_processor_id() for the `cpu' variable without breaking anything. Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20180706130615.g2ex2kmfu5kcvlq6@linutronix.de Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 13 ++++--------- 1 file changed, 4 insertions(+), 9 deletions(-) (limited to 'kernel/sched/core.c') diff --git a/kernel/sched/core.c b/kernel/sched/core.c index ba6bb805693a..c3cf7d992159 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2294,7 +2294,6 @@ static inline void init_schedstats(void) {} int sched_fork(unsigned long clone_flags, struct task_struct *p) { unsigned long flags; - int cpu = get_cpu(); __sched_fork(clone_flags, p); /* @@ -2330,14 +2329,12 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p) p->sched_reset_on_fork = 0; } - if (dl_prio(p->prio)) { - put_cpu(); + if (dl_prio(p->prio)) return -EAGAIN; - } else if (rt_prio(p->prio)) { + else if (rt_prio(p->prio)) p->sched_class = &rt_sched_class; - } else { + else p->sched_class = &fair_sched_class; - } init_entity_runnable_average(&p->se); @@ -2353,7 +2350,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p) * We're setting the CPU for the first time, we don't migrate, * so use __set_task_cpu(). */ - __set_task_cpu(p, cpu); + __set_task_cpu(p, smp_processor_id()); if (p->sched_class->task_fork) p->sched_class->task_fork(p); raw_spin_unlock_irqrestore(&p->pi_lock, flags); @@ -2370,8 +2367,6 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p) plist_node_init(&p->pushable_tasks, MAX_PRIO); RB_CLEAR_NODE(&p->pushable_dl_tasks); #endif - - put_cpu(); return 0; } -- cgit