Messages in this thread | | | Date | Wed, 10 Aug 2016 14:30:33 +0200 | From | Peter Zijlstra <> | Subject | Re: [patch] sched/cputime: Fix NO_HZ_FULL getrusage() monotonicity regression |
| |
On Wed, Aug 10, 2016 at 01:14:29PM +0200, Mike Galbraith wrote: > Hi Peter, > > While running ltp, the fates decided it was time for me to encounter > the roughly 1 out of every 10 call failure below. As much as I run > ltp, I'm a bit surprised that I (or anyone else) haven't met this > before, but then the fates are known to be a tad fickle. > > getrusage04 0 TINFO : Expected timers granularity is 4000 us > getrusage04 0 TINFO : Using 1 as multiply factor for max [us]time increment (1000+4000us)! > getrusage04 0 TINFO : utime: 0us; stime: 179us > getrusage04 0 TINFO : utime: 3751us; stime: 0us > getrusage04 1 TFAIL : getrusage04.c:133: stime increased > 5000us: > > When applying the full rtime to either stime or utime, do not overwrite > the previously tallied value. > > Fixes: 9d7fb0427648 ("sched/cputime: Guarantee stime + utime == rtime") > Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com> > Cc: stable@vger.kernel.org # 4.3+ > --- > kernel/sched/cputime.c | 2 ++ > 1 file changed, 2 insertions(+) > > --- a/kernel/sched/cputime.c > +++ b/kernel/sched/cputime.c > @@ -608,11 +608,13 @@ static void cputime_adjust(struct task_c > > if (utime == 0) { > stime = rtime; > + utime = prev->utime; > goto update; > } > > if (stime == 0) { > utime = rtime; > + stime = prev->stime; > goto update; > }
This cannot be right; it violates that utime+stime==rtime. Let me try and figure out what actually happens.
| |