From: Caesar Wang <wxt@rock-chips.com>
Date: Tue, 23 Aug 2016 10:47:02 +0000 (+0100)
Subject: sched/fair: remove printk while schedule is in progress
X-Git-Tag: firefly_0821_release~176^2~162
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=ca4b83c5476f68cb0ead77c23775e7ef68a37058;p=firefly-linux-kernel-4.4.55.git

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>
---

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 14c06f92184c..30d76a18ae1a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7125,7 +7125,8 @@ 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
 	}