On Mon May 8, 2023 at 12:01 PM AEST, Rohan McLure wrote:
> The power_save callback can be overwritten by another core at boot time.
> Specifically, null values will be replaced exactly once with the callback
> suitable for the particular platform (PowerNV / pseries lpars). Mark
> reads to this variable with READ_ONCE to signal to KCSAN that this race
> is acceptable, as well as to rule-out the possibility for compiler reorderings
> leading to calling a null pointer.
Is ppc_md readonly after init? Might be a good candidate if it is...
Maybe KCSAN doesn't recognise that though.
Unless the places that assign ppc_md.power_save need to be converted
to use WRITE_ONCE, you could just annotate this with data_race and
comment it's not really a race because it won't be called before the
structure is set up.
Thanks,
Nick
>
> Signed-off-by: Rohan McLure <rmcl...@linux.ibm.com>
> ---
> arch/powerpc/kernel/idle.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kernel/idle.c b/arch/powerpc/kernel/idle.c
> index b1c0418b25c8..a1589bb97c98 100644
> --- a/arch/powerpc/kernel/idle.c
> +++ b/arch/powerpc/kernel/idle.c
> @@ -43,10 +43,12 @@ __setup("powersave=off", powersave_off);
>
> void arch_cpu_idle(void)
> {
> + void (*power_save)(void) = READ_ONCE(ppc_md.power_save);
> +
> ppc64_runlatch_off();
>
> - if (ppc_md.power_save) {
> - ppc_md.power_save();
> + if (power_save) {
> + power_save();
> /*
> * Some power_save functions return with
> * interrupts enabled, some don't.
> --
> 2.37.2
