Re: [tip:timers/core] posix-timers: Zero out oldval itimerspec

Thomas Gleixner
2017-06-12T22:01:24Z

On Mon, 12 Jun 2017, Andrei Vagin wrote:
> > diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
> > index b53a0b5..88517dc 100644
> > --- a/kernel/time/posix-timers.c
> > +++ b/kernel/time/posix-timers.c
> > @@ -828,6 +828,8 @@ SYSCALL_DEFINE4(timer_settime, timer_t, timer_id, int, flags,
> > if (!timespec64_valid(&new_spec64.it_interval) ||
> > !timespec64_valid(&new_spec64.it_value))
> > return -EINVAL;
> > + if (rtn)
> > + memset(rtn, 0, sizeof(*rtn));
>
> Maybe we need to call memset after "retry:"?

That would be counter productive.

> common_timer_get() is called at the begining of common_timer_set(), then
> common_timer_set() can return TIMER_RETRY. common_timer_get() will be
> called again and some fields of rtn which have been touched first time
> will not be touched.
>
> At the end, rtn will contain data from two executions of
> common_timer_get().

No. See the full code sequence:

retry:
timr = lock_timer(timer_id, &flag);
if (!timr)
return -EINVAL;

kc = clockid_to_kclock(timr->it_clock);
if (WARN_ON_ONCE(!kc || !kc->timer_set))
error = -EINVAL;
else
error = kc->timer_set(timr, flags, &new_spec64, rtn);

unlock_timer(timr, flag);
if (error == TIMER_RETRY) {
rtn = NULL; // We already got the old time...
goto retry;
}

If you clear it after retry, you'll get all zeros in the retry case. Not
what you really want.

Thanks,

tglx