Messages in this thread | | | Subject | RE: PATCH: Fix race in cpu_down (hotplug cpu) | Date | Mon, 19 Sep 2005 12:48:38 +0800 | From | "Li, Shaohua" <> |
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Hi, > >On Mon, Sep 19, 2005 at 01:28:38PM +1000, Nigel Cunningham wrote: >> There is a race condition in taking down a cpu (kernel/cpu.c::cpu_down). >> A cpu can already be idling when we clear its online flag, and we do not >> force the idle task to reschedule. This results in __cpu_die timing out. > >"when we clear its online flag" - This happens in take_cpu_down in the >context of stopmachine thread. take_cpu_down also ensures that idle >thread runs when it returns (sched_idle_next). So when idle thread runs, >it should notice that it is offline and invoke play_dead. So I don't >understand why __cpu_die should time out. I guess Nigel's point is cpu_idle is preempted before take_cpu_down. If the preempt occurs after the cpu_is_offline check, when the cpu (after sched_idle_next) goes into idle again, nobody can wake it up. Nigel, isn't it?
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