mainline inclusion
from mainline-5.12-rc1
commit 29fd0194
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I410UT
CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=29fd01944b7273bb630c649a2104b7f9e4ef3fa6

---------------------------

DECLARE_STATIC_CALL() must pass the original function targeted for a
given static call. But DEFINE_STATIC_CALL() may want to initialize it as
off. In this case we can't pass NULL (for functions without return value)
or __static_call_return0 (for functions returning a value) directly
to DEFINE_STATIC_CALL() as that may trigger a static call redeclaration
with a different function prototype. Type casts neither can work around
that as they don't get along with typeof().

The proper way to do that for functions that don't return a value is
to use DEFINE_STATIC_CALL_NULL(). But functions returning a actual value
don't have an equivalent yet.

Provide DEFINE_STATIC_CALL_RET0() to solve this situation.
Signed-off-by: NFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NIngo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20210118141223.123667-3-frederic@kernel.orgSigned-off-by: NMa Junhai <majunhai2@huawei.com>
Reviewed-by: NChen Hui <judy.chenhui@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>