Re: [Minios-devel] [UNIKRAFT PATCH 2/8] lib/uksched: Do not reset sched attribute on thread removal

[Florian Schmidt <Florian.Schmidt@xxxxxxxxx>]

Hi Costin,

could you give a short explanation what the semantics of t->sched and 
setting it to NULL is? Is this value actually used (and expected to be 
non-null) at a later stage during the thread teardown? I first though 
"oh, uk_sched_thread_destroy() probably wants to look up the scheduler, 
but wait, how could this ever have worked then?", but it is called from 
the main scheduler loop and so gets the scheduler info from there 
instead of the thread.
So, I'm wondering whether I'm missing something. Sure, a superfluous 
call to setting something to null is extra work for no gain (and 
arguably it's semantically wrong, because the thread still kinda is 
assigned to the scheduler, if only because it's the scheduler's job to 
clean up the thread), but is there something more pressing and buggy 
that I'm missing?
Cheers,
Florian

On 4/23/19 12:41 PM, Costin Lupu wrote:
> Scheduler reference should be kept until destroying the thread,
> basically during the entire life of the thread. uk_sched_thread_remove()
> is always called before destroying the thread, therefore it must not
> remove the scheduler reference from thread.
>
> Signed-off-by: Costin Lupu <costin.lupu@xxxxxxxxx>
> ---
>   lib/uksched/include/uk/sched.h | 1 -
>   1 file changed, 1 deletion(-)
>
> diff --git a/lib/uksched/include/uk/sched.h b/lib/uksched/include/uk/sched.h
> index cc5fbe93..f9dc16d0 100644
> --- a/lib/uksched/include/uk/sched.h
> +++ b/lib/uksched/include/uk/sched.h
> @@ -130,7 +130,6 @@ static inline int uk_sched_thread_remove(struct uk_sched *s,
>         UK_ASSERT(t);
>         UK_ASSERT(t->sched == s);
>         s->thread_remove(s, t);
> -       t->sched = NULL;
>         return 0;
>   }
>   
--
Dr. Florian Schmidt
フローリアン・シュミット
Research Scientist,
Systems and Machine Learning Group
NEC Laboratories Europe
Kurfürsten-Anlage 36, D-69115 Heidelberg
Tel.     +49 (0)6221 4342-265
Fax:     +49 (0)6221 4342-155
e-mail:  florian.schmidt@xxxxxxxxx
============================================================
Registered at Amtsgericht Mannheim, Germany, HRB728558

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