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SubjectRe: [PATCH] cpu/hotplug: Fix rollback during error-out in takedown_cpu()

On 09/05/2018 06:47 PM, Thomas Gleixner wrote:
> On Wed, 5 Sep 2018, Neeraj Upadhyay wrote:
>> On 09/05/2018 05:53 PM, Thomas Gleixner wrote:
>>> And looking closer this is a general issue. Just that the TEARDOWN state
>>> makes it simple to observe. It's universaly broken, when the first teardown
>>> callback fails because, st->state is only decremented _AFTER_ the callback
>>> returns success, but undo_cpu_down() increments unconditionally.
>> As per my understanding, there are 2 problems here; one is fixed with your
>> patch, and other is cpuhp_reset_state() is used during rollback from non-AP to
>> AP state, which seem to result in 2 increments of st->state (one increment
>> done by cpuhp_reset_state() and another by cpu_thread_fun()) .
> And how did your hack fix that up magically? I'll have a look later today.
> Thanks,
> tglx

The hack fixes it by not calling cpuhp_reset_state() and doing rollback
state reset inline in  _cpu_down().

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