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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 7eab14de73 ("mdio, phy: fix -Wshadow warnings triggered by
nested container_of()")
- commit 8d8c313124 ("clk: define to_clk_regmap() as inline
function")
- commit bfb972c5e1 ("IB/verbs: avoid nested container_of()")
- commit 093adbcedf ("btrfs: switch helper macros to static inlines
in sysfs.h")
- commit c1d35dfa0f ("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>
40 lines
1.4 KiB
40 lines
1.4 KiB