On Wed, 13 Nov 2013 10:03:37 +0100, Pantelis Antoniou <panto@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
> On Nov 13, 2013, at 2:34 AM, Grant Likely wrote:
> > On Tue, 12 Nov 2013 11:39:08 +0100, Pantelis Antoniou <panto@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
> >>> On Tue, 5 Nov 2013 19:50:16 +0200, Pantelis Antoniou <panto@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
> >>>> + } else {
> >>>> + pr_warn("%s: node %p cannot be freed; memory is gone\n",
> >>>> + __func__, node);
> >>>> + }
> >>>> +}
> >>>
> >>> All of the above is potentially dangerous. There is no way to determine
> >>> if anything still holds a reference to a node. The proper way to handle
> >>> removal of properties is to have a release method when the last
> >>> of_node_put is called.
> >>>
> >>
> >> This is safe, and expected to be called only on a dynamically created tree,
> >> that's what all the checks against OF_DYNAMIC guard against.
> >>
> >> It is not ever meant to be called on an arbitrary tree, created by unflattening
> >> a blob.
> >
> > I am talking about when being used on a dynamic tree. The problem is
> > when a driver or other code holds a reference to a dynamic nodes, but
> > doesn't release it correctly. The memory must not be freed until all of
> > the references are relased. OF_DYNAMIC doesn't actually help in that
> > case, and it is the reason for of_node_get()/of_node_put()
> >
>
> I know, but even that is not enough. of_node_get()/of_node_put() handles the
> case of references to the nodes, but not what happens with references to
> properties. deadprops is mitigating the problem somewhat, but if we're going
> to go to all the trouble of kobjectification let's do the props as well.
>
> of_get_property could be modified to return a devm_kmalloced copy of the real
> property and that would deal with most of the callers. Of course for
> the small sized scalar data we can avoid the copy.
>
> By using the devm_* interface we also avoid having to mess too much with the callers.
>
> I.e. what about something like devm_of_get_property()?
Reference counting is already a horrible pain to keep correct. I don't
see a better way to handle it in the dynamic case, so we're stuck with
it, but I don't want to make it any harder. Adding ref counting to
properties will make it harder than it already is to get the code right.
I'm absolutely fine with a little bit of wasted memory in the form of
deadprops when the alternative is so horrible. References at the node
level is enough granularity.
I don't think kduping the property is the solution either. I strongly
suspect that will be far more expensive than the deadprop solution.
> >>>> +{
> >>>> + struct device_node *node;
> >>>> +
> >>>> + node = kzalloc(sizeof(*node), flags);
> >>>> + if (node == NULL)
> >>>> + return NULL;
> >>>> +
> >>>> + node->name = kstrdup(name, flags);
> >>>> + if (node->name == NULL)
> >>>> + goto err_return;
> >>>> +
> >>>> + node->type = kstrdup(type, flags);
> >>>> + if (node->type == NULL)
> >>>> + goto err_return;
> >>>> +
> >>>> + node->full_name = kstrdup(full_name, flags);
> >>>> + if (node->type == NULL)
> >>>> + goto err_return;
> >>>
> >>> Again, who do you expect the user of this function to be? If it is part
> >>> of unflattening an overlay tree, is there a reason that the passed in
> >>> names cannot be used directly instead of kmallocing them?
> >>>
> >>
> >> I want to be able to get rid of the blob eventually; I don't need to keep
> >> dragging it around.
> >
> > Why? It really doesn't hurt and it means data does not need to be
> > copied.
>
> Copying data lead to less problems that having to drag that blob around.
> That's just preference, so not a big issue.
Can you elaborate? What problems do you foresee being created by keeping
the blob?
g.
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
