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sched: make early bootup sched_clock() use safer

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do not call sched_clock() too early. Not only might rq->idle
not be set up - but pure per-cpu data might not be accessible
either.

this solves an ia64 early bootup hang with CONFIG_PRINTK_TIME=y.

Tested-by: Tony Luck <tony.luck@gmail.com>
Acked-by: Tony Luck <tony.luck@gmail.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Ingo Molnar
2008-02-13 14:02:36 +01:00
parent bfa274e243
commit 6892b75e60
1 changed files with 10 additions and 4 deletions
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14
kernel/sched.c
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@@ -668,6 +668,8 @@ const_debug unsigned int sysctl_sched_nr_migrate = 32;
*/ */
unsigned int sysctl_sched_rt_period = 1000000; unsigned int sysctl_sched_rt_period = 1000000;
static __read_mostly int scheduler_running;
/* /*
* part of the period that we allow rt tasks to run in us. * part of the period that we allow rt tasks to run in us.
* default: 0.95s * default: 0.95s
@@ -689,14 +691,16 @@ unsigned long long cpu_clock(int cpu)
unsigned long flags; unsigned long flags;
struct rq *rq; struct rq *rq;
local_irq_save(flags);
rq = cpu_rq(cpu);
/* /*
* Only call sched_clock() if the scheduler has already been * Only call sched_clock() if the scheduler has already been
* initialized (some code might call cpu_clock() very early): * initialized (some code might call cpu_clock() very early):
*/ */
if (rq->idle) if (unlikely(!scheduler_running))
update_rq_clock(rq); return 0;
local_irq_save(flags);
rq = cpu_rq(cpu);
update_rq_clock(rq);
now = rq->clock; now = rq->clock;
local_irq_restore(flags); local_irq_restore(flags);
@@ -7284,6 +7288,8 @@ void __init sched_init(void)
* During early bootup we pretend to be a normal task: * During early bootup we pretend to be a normal task:
*/ */
current->sched_class = &fair_sched_class; current->sched_class = &fair_sched_class;
scheduler_running = 1;
} }
#ifdef CONFIG_DEBUG_SPINLOCK_SLEEP #ifdef CONFIG_DEBUG_SPINLOCK_SLEEP