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  1. 13 Mar, 2024 2 commits
    • Jonathan Cameron's avatar
      of: Introduce for_each_*_child_of_node_scoped() to automate of_node_put() handling · 34af4554
      Jonathan Cameron authored 
      To avoid issues with out of order cleanup, or ambiguity about when the
auto freed data is first instantiated, do it within the for loop definition.

The disadvantage is that the struct device_node *child variable creation
is not immediately obvious where this is used.
However, in many cases, if there is another definition of
struct device_node *child; the compiler / static analysers will notify us
that it is unused, or uninitialized.

Note that, in the vast majority of cases, the _available_ form should be
used and as code is converted to these scoped handers, we should confirm
that any cases that do not check for available have a good reason not
to.
Signed-off-by: default avatarJonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: default avatarRob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20240225142714.286440-3-jic23@kernel.orgSigned-off-by: default avatarRob Herring <robh@kernel.org>
      34af4554
    • Jonathan Cameron's avatar
      of: Add cleanup.h based auto release via __free(device_node) markings · 9448e55d
      Jonathan Cameron authored 
      The recent addition of scope based cleanup support to the kernel
provides a convenient tool to reduce the chances of leaking reference
counts where of_node_put() should have been called in an error path.

This enables
	struct device_node *child __free(device_node) = NULL;

	for_each_child_of_node(np, child) {
		if (test)
			return test;
	}

with no need for a manual call of of_node_put().
A following patch will reduce the scope of the child variable to the
for loop, to avoid an issues with ordering of autocleanup, and make it
obvious when this assigned a non NULL value.

In this simple example the gains are small but there are some very
complex error handling cases buried in these loops that will be
greatly simplified by enabling early returns with out the need
for this manual of_node_put() call.

Note that there are coccinelle checks in
scripts/coccinelle/iterators/for_each_child.cocci to detect a failure
to call of_node_put(). This new approach does not cause false positives.
Longer term we may want to add scripting to check this new approach is
done correctly with no double of_node_put() calls being introduced due
to the auto cleanup. It may also be useful to script finding places
this new approach is useful.
Signed-off-by: default avatarJonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: default avatarRob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20240225142714.286440-2-jic23@kernel.orgSigned-off-by: default avatarRob Herring <robh@kernel.org>
      9448e55d
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