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sched: fix cpu hotplug
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>
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@ -5621,8 +5621,10 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
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double_rq_lock(rq_src, rq_dest);
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/* Already moved. */
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if (task_cpu(p) != src_cpu)
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if (task_cpu(p) != src_cpu) {
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ret = 1;
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goto out;
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}
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/* Affinity changed (again). */
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if (!cpu_isset(dest_cpu, p->cpus_allowed))
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goto out;
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