Messages in this thread | | | From | Ulf Hansson <> | Date | Wed, 12 Jan 2022 13:00:09 +0100 | Subject | Re: [PATCH v5 2/6] powercap/drivers/dtpm: Add hierarchy creation |
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On Tue, 11 Jan 2022 at 18:52, Daniel Lezcano <daniel.lezcano@linaro.org> wrote: > > On 11/01/2022 09:28, Ulf Hansson wrote: > > On Mon, 10 Jan 2022 at 16:55, Daniel Lezcano <daniel.lezcano@linaro.org> wrote: > >> > >> On 07/01/2022 16:54, Ulf Hansson wrote: > >>> [...] > >>> > >>>>>> +static int dtpm_for_each_child(const struct dtpm_node *hierarchy, > >>>>>> + const struct dtpm_node *it, struct dtpm *parent) > >>>>>> +{ > >>>>>> + struct dtpm *dtpm; > >>>>>> + int i, ret; > >>>>>> + > >>>>>> + for (i = 0; hierarchy[i].name; i++) { > >>>>>> + > >>>>>> + if (hierarchy[i].parent != it) > >>>>>> + continue; > >>>>>> + > >>>>>> + dtpm = dtpm_node_callback[hierarchy[i].type](&hierarchy[i], parent); > >>>>>> + if (!dtpm || IS_ERR(dtpm)) > >>>>>> + continue; > >>>>>> + > >>>>>> + ret = dtpm_for_each_child(hierarchy, &hierarchy[i], dtpm); > >>>>> > >>>>> Why do you need to recursively call dtpm_for_each_child() here? > >>>>> > >>>>> Is there a restriction on how the dtpm core code manages adding > >>>>> children/parents? > >>>> > >>>> [ ... ] > >>>> > >>>> The recursive call is needed given the structure of the tree in an array > >>>> in order to connect with the parent. > >>> > >>> Right, I believe I understand what you are trying to do here, but I am > >>> not sure if this is the best approach to do this. Maybe it is. > >>> > >>> The problem is that we are also allocating memory for a dtpm and we > >>> call dtpm_register() on it in this execution path - and this memory > >>> doesn't get freed up nor unregistered, if any of the later recursive > >>> calls to dtpm_for_each_child() fails. > >>> > >>> The point is, it looks like it can get rather messy with the recursive > >>> calls to cope with the error path. Maybe it's easier to store the > >>> allocated dtpms in a list somewhere and use this to also find a > >>> reference of a parent? > >> > >> I think it is better to continue the construction with other nodes even > >> some of them failed to create, it should be a non critical issue. As an > >> analogy, if one thermal zone fails to create, the other thermal zones > >> are not removed. > > > > Well, what if it fails because its "consumer part" is waiting for some > > resource to become available? > > > > Maybe the devfreq driver/subsystem isn't available yet and causes > > -EPROBE_DEFER, for example. Perhaps this isn't the way the dtpm > > registration works currently, but sure it's worth considering when > > going forward, no? > > It should be solved by the fact that the DTPM description is a module > and loaded after the system booted. The module loading ordering is > solved by userspace.
Ideally, yes. However, drivers/subsystems in the kernel should respect -EPROBE_DEFER. It's good practice to do that.
> > I agree, we could improve that but it is way too complex to be addressed > in a single series and should be part of a specific change IMO.
It's not my call to make, but I don't agree, sorry.
In my opinion, plain error handling to avoid leaking memory isn't something that should be addressed later. At least if the problems are already spotted during review.
> > > In any case, papering over the error seems quite scary to me. I would > > much prefer if we instead could propagate the error code correctly to > > the caller of dtpm_create_hierarchy(), to allow it to retry if > > necessary. > > It is really something we should be able to address later. >
[...]
Kind regards Uffe
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