[PATCH] x86/efi: mark racy access on efi_rts_work.efi_rts_id

[PATCH] x86/efi: mark racy access on efi_rts_work.efi_rts_id

[linke li]

In efi_crash_gracefully_on_page_fault(), efi_rts_work.efi_rts_id can by
changed by other thread from the comment. Mark possible data race on 
efi_rts_work.efi_rts_id as benign using READ_ONCE.

This patch is aimed at reducing the number of benign races reported by
KCSAN in order to focus future debugging effort on harmful races.

Signed-off-by: linke li <lilinke99@qq.com>
---
 arch/x86/platform/efi/quirks.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
index f0cc00032751..4acb81700caf 100644
--- a/arch/x86/platform/efi/quirks.c
+++ b/arch/x86/platform/efi/quirks.c
@@ -751,7 +751,7 @@ void efi_crash_gracefully_on_page_fault(unsigned long phys_addr)
 	 * because this case occurs *very* rarely and hence could be improved
 	 * on a need by basis.
 	 */
-	if (efi_rts_work.efi_rts_id == EFI_RESET_SYSTEM) {
+	if (READ_ONCE(efi_rts_work.efi_rts_id) == EFI_RESET_SYSTEM) {
 		pr_info("efi_reset_system() buggy! Reboot through BIOS\n");
 		machine_real_restart(MRR_BIOS);
 		return;
-- 
2.39.3 (Apple Git-146)

Re: [PATCH] x86/efi: mark racy access on efi_rts_work.efi_rts_id

[Ard Biesheuvel]

On Sat, 27 Apr 2024 at 07:28, linke li <lilinke99@qq.com> wrote:
>
> In efi_crash_gracefully_on_page_fault(), efi_rts_work.efi_rts_id can by
> changed by other thread from the comment. Mark possible data race on
> efi_rts_work.efi_rts_id as benign using READ_ONCE.
>
> This patch is aimed at reducing the number of benign races reported by
> KCSAN in order to focus future debugging effort on harmful races.
>
> Signed-off-by: linke li <lilinke99@qq.com>
> ---
>  arch/x86/platform/efi/quirks.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
> index f0cc00032751..4acb81700caf 100644
> --- a/arch/x86/platform/efi/quirks.c
> +++ b/arch/x86/platform/efi/quirks.c
> @@ -751,7 +751,7 @@ void efi_crash_gracefully_on_page_fault(unsigned long phys_addr)
>          * because this case occurs *very* rarely and hence could be improved
>          * on a need by basis.
>          */
> -       if (efi_rts_work.efi_rts_id == EFI_RESET_SYSTEM) {
> +       if (READ_ONCE(efi_rts_work.efi_rts_id) == EFI_RESET_SYSTEM) {
>                 pr_info("efi_reset_system() buggy! Reboot through BIOS\n");
>                 machine_real_restart(MRR_BIOS);
>                 return;

Why is this the only reference that needs an annotation?

Re: [PATCH] x86/efi: mark racy access on efi_rts_work.efi_rts_id

[linke li]

> Why is this the only reference that needs an annotation?

In the function efi_runtime_services_init(), the if check on
efi_rts_work.efi_rts_id in line 728 uses READ_ONCE(), and the comment
explains that this is to reduce reports from KTSAN.

I propose that the check in line 754 undergoes a similar treatment for
consistency and to potentially reduce sanitizer reports.

Thank you.