Re: [PATCH v2 2/3] kcsan: mark !__SANITIZE_THREAD__ stub __always_inline

[Marco Elver]

On Mon, 15 Dec 2025 at 11:12, Brendan Jackman <jackmanb@xxxxxxxxxx> wrote:
>
> The x86 instrumented bitops in
> include/asm-generic/bitops/instrumented-non-atomic.h are
> KCSAN-instrumented via explicit calls to instrument_* functions from
> include/linux/instrumented.h.
>
> This bitops are used from noinstr code in __sev_es_nmi_complete(). This
> code avoids noinstr violations by disabling __SANITIZE_THREAD__ etc for
> the compilation unit.
>
> However, when GCOV is enabled, there can still be violations caused by
> the stub versions of these functions, since coverage instrumentation is
> injected that causes them to be out-of-lined.
>
> Fix this by just applying __always_inline.
>
> Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx>
> ---
>  include/linux/kcsan-checks.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/kcsan-checks.h b/include/linux/kcsan-checks.h
> index 92f3843d9ebb8177432bb4eccc151ea66d3dcbb7..cabb2ae46bdc0963bd89533777cab586ab4d5a1b 100644
> --- a/include/linux/kcsan-checks.h
> +++ b/include/linux/kcsan-checks.h
> @@ -226,7 +226,7 @@ static inline void kcsan_end_scoped_access(struct kcsan_scoped_access *sa) { }
>  #define __kcsan_disable_current kcsan_disable_current
>  #define __kcsan_enable_current kcsan_enable_current_nowarn
>  #else /* __SANITIZE_THREAD__ */
> -static inline void kcsan_check_access(const volatile void *ptr, size_t size,
> +static __always_inline void kcsan_check_access(const volatile void *ptr, size_t size,
>                                       int type) { }
>  static inline void __kcsan_enable_current(void)  { }
>  static inline void __kcsan_disable_current(void) { }

It wouldn't be wrong to apply __always_inline to these 2 stub
functions as well, but I think it's fair if you just limit this to the
ones used from <linux/instrumented.h>. Either way, please
double-check.