svn commit: r222060 - in user/avg/xcpu/sys: kern sys

[Attilio Rao]

2011/5/18  <mdf at freebsd.org>:
> On Wed, May 18, 2011 at 1:06 PM, Attilio Rao <attilio at freebsd.org> wrote:
>> 2011/5/18 Andriy Gapon <avg at freebsd.org>:
>>> on 18/05/2011 21:24 Pawel Jakub Dawidek said the following:
>>>> On Wed, May 18, 2011 at 03:08:30PM +0000, Andriy Gapon wrote:
>>>> [...]
>>>>> --- user/avg/xcpu/sys/sys/proc.h     Wed May 18 15:07:36 2011        (r222059)
>>>>> +++ user/avg/xcpu/sys/sys/proc.h     Wed May 18 15:08:30 2011        (r222060)
>>>>> @@ -781,7 +781,7 @@ MALLOC_DECLARE(M_SUBPROC);
>>>>>   * Otherwise, the kernel will deadlock since the scheduler isn't
>>>>>   * going to run the thread that holds the lock we need.
>>>>>   */
>>>>> -#define     THREAD_PANICED()        \
>>>>> +#define     TD_IS_INPANIC() \
>>>>>      (panicstr != NULL && (curthread->td_flags & TDF_INPANIC) != 0)
>>>>
>>>> Does TDF_INPANIC make sense without panicstr being set?
>>>
>>> Very good observation.  It seems that TDF_INPANIC can never be set unless
>>> panicstr is set.  So, I guess it should be OK to simplify the macro further.
>>> Thank you.
>>
>> However I think that TDF_INPANIC handling is not optimal.
>> You should really acquire thread_lock otherwise you are going to break
>> choosethread() concurrency.
>>
>> I would prefer to make TDF_INPANIC a private flag and just use it with
>> curthread, if possible, but I still don't have a good way to resolve
>> choosethread() (I would dig the runqueue adding path and resolve the
>> problem later in the codeflow, I think).
>
> I know it's almost required now (sync on reboot?!?!), but I would
> strongly question, from an architectural standpoint, why the scheduler
> should be running at all in panic.  Once a thread pulls the panic
> trigger, nothing else should run except ddb in that thread's context.

Yes, I mostly agree, so for avg's purpose he should maybe assert
choosethread() doesn't pickup the TDF_INPANIC threads (or just skip
the check at all, as it should be made private).

Attilio


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