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sched: fix cpu hotplug

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I think we may have a race between try_to_wake_up() and
migrate_live_tasks() -> move_task_off_dead_cpu() when the later one
may end up looping endlessly.

Interrupts are enabled on other CPUs when migration_call(CPU_DEAD, ...) is
called so we may get a race between try_to_wake_up() and
migrate_live_tasks() -> move_task_off_dead_cpu(). The former one may push
a task out of a dead CPU causing the later one to loop endlessly.

Heiko Carstens observed:

| That's exactly what explains a dump I got yesterday. Thanks for fixing! :)

Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Cc: miaox@cn.fujitsu.com
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Avi Kivity <avi@qumranet.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Dmitry Adamushko 2008-07-10 00:32:40 +02:00 committed by Ingo Molnar
parent 619b048803
commit dc7fab8b3b
1 changed files with 3 additions and 1 deletions
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4
kernel/sched.c
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@ -5621,8 +5621,10 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
double_rq_lock(rq_src, rq_dest); double_rq_lock(rq_src, rq_dest);
/* Already moved. */ /* Already moved. */
if (task_cpu(p) != src_cpu) if (task_cpu(p) != src_cpu) {
ret = 1;
goto out; goto out;
}
/* Affinity changed (again). */ /* Affinity changed (again). */
if (!cpu_isset(dest_cpu, p->cpus_allowed)) if (!cpu_isset(dest_cpu, p->cpus_allowed))
goto out; goto out;