container_of: remove local __mptr variable

container_of() can be called in a nested manner to retrieve the grand
parent structure as illustrated below:

	struct foo {
		int a;
	};

	struct bar {
		struct foo foo;
	};

	#define to_foo(a_ptr) container_of(a_ptr, struct foo, a)
	#define to_bar(a_ptr) container_of(to_foo(a_ptr), struct bar, foo)

The issue is that the above construct will cause __mptr, the local
variable of container_of(), to shadow itself because of the nested
call. This then triggers a warning in sparse and W=2 builds.

While this warning is benign, it still causes some overhead as proven by
below list of commits in which people made local workarounds:

  - commit 7eab14de73a8 ("mdio, phy: fix -Wshadow warnings triggered by
    nested container_of()")

  - commit 8d8c3131248d ("clk: define to_clk_regmap() as inline
    function")

  - commit bfb972c5e1cb ("IB/verbs: avoid nested container_of()")

  - commit 093adbcedf12 ("btrfs: switch helper macros to static inlines
    in sysfs.h")

  - commit c1d35dfa0f7d ("rt2x00: Fix sparse warning on nested
    container_of()")

(the list is probably not exhaustive).

As a matter of fact, the local variable __mptr is only used once in
container_of(). As such, it is not strictly needed. Inline that local
__mptr variable to remove once and for all the risk of variable
shadowing when nesting container_of() and prevent people from writing
further local fixes.

Signed-off-by: Vincent Mailhol <mailhol@kernel.org>
Link: https://patch.msgid.link/20260714-containerof_refactor-v1-3-b5c31164d2ad@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

0 files changed, 0 insertions, 0 deletions