Messages in this thread | | | Date | Fri, 5 Oct 2018 08:00:23 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH 2/3] x86/vdso: Rearrange do_hres() to improve code generation |
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On Thu, 4 Oct 2018, Andy Lutomirski wrote: > index 18c8a78d1ec9..419de7552c2f 100644 > --- a/arch/x86/entry/vdso/vclock_gettime.c > +++ b/arch/x86/entry/vdso/vclock_gettime.c > @@ -147,10 +147,9 @@ notrace static int do_hres(clockid_t clk, struct timespec *ts) > > do { > seq = gtod_read_begin(gtod); > - ts->tv_sec = base->sec; > + cycles = vgetcyc(gtod->vclock_mode); > ns = base->nsec; > last = gtod->cycle_last; > - cycles = vgetcyc(gtod->vclock_mode); > if (unlikely((s64)cycles < 0)) > return vdso_fallback_gettime(clk, ts); > if (cycles > last) > @@ -158,7 +157,7 @@ notrace static int do_hres(clockid_t clk, struct timespec *ts) > ns >>= gtod->shift; > } while (unlikely(gtod_read_retry(gtod, seq))); > > - ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns); > + ts->tv_sec = base->sec + __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
You cannot access base->sec outside of the seqcount protected region. It might have been incremented by now and you'll get a time jump by a full second.
Thanks,
tglx
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