Subject: Re: [RFC PATCH v2 07/10] lib: vdso: don't use READ_ONCE() in __c_kernel_time()

From: Thomas Gleixner <[email-masked]>
Date: Fri, 10 Jan 2020 22:12:06 +0100

Christophe Leroy <[email-masked]> writes:
>
> diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
> index 17b4cff6e5f0..5a17a9d2e6cd 100644
> --- a/lib/vdso/gettimeofday.c
> +++ b/lib/vdso/gettimeofday.c
> @@ -144,7 +144,7 @@ __cvdso_gettimeofday(const struct vdso_data *vd, struct __kernel_old_timeval *tv
>  static __maybe_unused __kernel_old_time_t
>  __cvdso_time(const struct vdso_data *vd, __kernel_old_time_t *time)
>  {
> -	__kernel_old_time_t t = READ_ONCE(vd[CS_HRES_COARSE].basetime[CLOCK_REALTIME].sec);
> +	__kernel_old_time_t t = vd[CS_HRES_COARSE].basetime[CLOCK_REALTIME].sec;
>  
>  	if (time)
>  		*time = t;

Allows the compiler to load twice, i.e. the returned value might be different from the
stored value. So no.

Thanks,

        tglx