Commit baf25731 authored Sep 09, 2008 by Zhang, Yanmin Committed by Ingo Molnar Sep 11, 2008

sched: fix 2.6.27-rc5 couldn't boot on tulsa machine randomly



On my tulsa x86-64 machine, kernel 2.6.25-rc5 couldn't boot randomly.

Basically, function __enable_runtime forgets to reset rt_rq->rt_throttled
to 0. When every cpu is up, per-cpu migration_thread is created and it runs
very fast, sometimes to mark the corresponding rt_rq->rt_throttled to 1 very
quickly. After all cpus are up, with below calling chain:

   sched_init_smp => arch_init_sched_domains => build_sched_domains => ...
=> cpu_attach_domain => rq_attach_root => set_rq_online => ...
=> _enable_runtime

_enable_runtime is called against every rt_rq again, so rt_rq->rt_time is
reset to 0, but rt_rq->rt_throttled might be still 1. Later on function
do_sched_rt_period_timer couldn't reset it, and all RT tasks couldn't be
scheduled to run on that cpu. here is RT task migration_thread which is
woken up when a task is migrated to another cpu.

Below patch fixes it against 2.6.27-rc5.

Signed-off-by: Zhang Yanmin <yanmin_zhang@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 291c54ff

kernel/sched_rt.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -350,6 +350,7 @@ static void __enable_runtime(struct rq *rq)
		spin_lock(&rt_rq->rt_runtime_lock);
		rt_rq->rt_runtime = rt_b->rt_runtime;
		rt_rq->rt_time = 0;
		rt_rq->rt_throttled = 0;
		spin_unlock(&rt_rq->rt_runtime_lock);
		spin_unlock(&rt_b->rt_runtime_lock);
		}

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