On Tue, 16 Jan 2024 12:26:49 -0600
Rob Herring <robh@xxxxxxxxxx> wrote:
> On Sun, Jan 14, 2024 at 10:54 AM Jonathan Cameron <jic23@xxxxxxxxxx> wrote:
> >
> > From: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> >
> > A simple example of the utility of this autocleanup approach to
> > handling of_node_put()
> >
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> > ---
> > drivers/of/unittest.c | 10 +++-------
> > 1 file changed, 3 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
> > index e9e90e96600e..b6d9edb831f0 100644
> > --- a/drivers/of/unittest.c
> > +++ b/drivers/of/unittest.c
> > @@ -233,27 +233,23 @@ static void __init of_unittest_dynamic(void)
> >
> > static int __init of_unittest_check_node_linkage(struct device_node *np)
> > {
> > - struct device_node *child;
> > + struct device_node *child __free(device_node) = NULL;
>
> In another thread[1], it seems that initializing to NULL is bad form
> according to the chief penguin. But as this is a refcounted pointer
> rather than an allocation, IDK?
I'm not sure the argument applies here. My understanding is it's not
really about the = NULL, but more about where the __free(device_node) is.
The ordering of that cleanup wrt to other similar clean up is to do it
in reverse order of declaration and in some cases that might cause trouble.
Here, the only way we could ensure the allocation was done at the right
point and we didn't have that __free before it was set, would be to add
variants of for_each_child_of_node() etc that did something like
#define for_each_child_of_node_scoped(parent, child) \
for (struct device_node *child __free(device_node) = \
of_get_next_child(parent, NULL); \
child != NULL; \
child = of_get_next_child(parent, child))
So that the child variable doesn't exist at all outside of the scope
of the loop.
I thought about proposing that style of solution but it felt more invasive
than a simple __free() annotation. I don't mind going that way though
if you prefer it.
Alternative is just to make sure the struct device_node * is always
declared just before the for loop and not bother setting it to NULL
(which is pointless anyway - it just felt fragile to not do so!)
Jonathan
>
> Rob
>
> [1] https://lore.kernel.org/all/289c4af00bcc46e83555dacbc76f56477126d645.camel@xxxxxxxxxxxxxx
