Re: [PATCH 1/2] stop_machine: check work->done while handlingenqueued works

[Hillf Danton]

On Sun, Feb 10, 2013 at 3:08 AM, Tejun Heo <tj@xxxxxxxxxx> wrote:
> Hello, Hillf.
>
> On Fri, Feb 08, 2013 at 11:39:56AM +0800, Hillf Danton wrote:
>> The comment just above cpu_stop_signal_done() says it is uncertain that
>> the input @done is valid, and the works enqueued through the function
>> stop_one_cpu_nowait() do carry no done, thus we have to check if it is
>> valid when updating work result.
>
> How about something like the following?

Cool, I like it, thanks.

Hillf
>
> In cpu_stopper_thread(), @work->done may be NULL if the cpu stop work
> is queued from stop_one_cpu_nowait(); however, cpu_stopper_thread()
> updates @done->ret without checking whether @done exists or not when
> the work function fails.
>
> While this can lead to oops, the only current user of
> stop_one_cpu_nowait() - active_load_balance_cpu_stop() - always
> returns 0 and thus there's no in-kernel user which triggers this bug.
>
> Fix it by checking whether @done exists before updating @done->ret.
>
>> Signed-off-by: Hillf Danton <dhillf@xxxxxxxxx>
>> ---
>>
>> --- a/kernel/stop_machine.c   Thu Feb  7 20:03:10 2013
>> +++ b/kernel/stop_machine.c   Fri Feb  8 11:07:40 2013
>> @@ -279,7 +279,7 @@ repeat:
>>               preempt_disable();
>>
>>               ret = fn(arg);
>> -             if (ret)
>> +             if (ret && done != NULL)
>
> It's a nitpick and probalby is just a preference but I've never liked
> != NULL or != 0.  Can we just do if (ret && done)?
>
> Thanks.
>
> --
> tejun
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