Commit df232437 authored Aug 23, 2016 by Caesar Wang Committed by Todd Kjos Sep 21, 2016

sched/fair: remove printk while schedule is in progress



It will cause deadlock and while(1) if call printk while schedule is in
progress. The block state like as below:

cpu0(hold the console sem):
printk->console_unlock->up_sem->spin_lock(&sem->lock)->wake_up_process(cpu1)
->try_to_wake_up(cpu1)->while(p->on_cpu).

cpu1(request console sem):
console_lock->down_sem->schedule->idle_banlance->update_cpu_capacity->
printk->console_trylock->spin_lock(&sem->lock).

p->on_cpu will be 1 forever, because the task is still running on cpu1,
so cpu0 is blocked in while(p->on_cpu), but cpu1 could not get
spin_lock(&sem->lock), it is blocked too, it means the task will running
on cpu1 forever.

Signed-off-by: Caesar Wang <wxt@rock-chips.com>

parent 32cbbe59

kernel/sched/fair.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -7089,7 +7089,8 @@ static void update_cpu_capacity(struct sched_domain *sd, int cpu)
		mcc->cpu = cpu;
		#ifdef CONFIG_SCHED_DEBUG
		raw_spin_unlock_irqrestore(&mcc->lock, flags);
		pr_info("CPU%d: update max cpu_capacity %lu\n", cpu, capacity);
		printk_deferred(KERN_INFO "CPU%d: update max cpu_capacity %lu\n",
		cpu, capacity);
		goto skip_unlock;
		#endif
		}