Messages in this thread Patch in this message | | | Subject | PATCH: Fix race in cpu_down (hotplug cpu) | From | Nigel Cunningham <> | Date | Mon, 19 Sep 2005 13:28:38 +1000 |
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Hmm... managed to miss a word at the end of the first para and thus not make sense. Let's try again.
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Hi.
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. A simple fix is to force the idle task on the cpu going down to reschedule.
Without the patch below, Suspend2 get into a deadlock at resume time when this issue occurs. I could not complete 20 cycles without seeing the issue. With the patch below, I have completed 75 cycles on the trot without problems.
Please apply.
Signed-off-by: Nigel Cunningham <ncunningham@cyclades.com>
diff -ruNp 9910-hotplug-cpu-race.patch-old/kernel/cpu.c 9910-hotplug-cpu-race.patch-new/kernel/cpu.c --- 9910-hotplug-cpu-race.patch-old/kernel/cpu.c 2005-08-29 10:29:58.000000000 +1000 +++ 9910-hotplug-cpu-race.patch-new/kernel/cpu.c 2005-09-19 12:15:08.000000000 +1000 @@ -126,6 +126,9 @@ int cpu_down(unsigned int cpu) while (!idle_cpu(cpu)) yield(); + /* CPU may have idled before we set its offline flag. */ + set_tsk_need_resched(idle_task(cpu)); + /* This actually kills the CPU. */ __cpu_die(cpu);
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