On Tue, Sep 06, 2016 at 09:01:29PM +0200, Peter Zijlstra wrote:
> On Tue, Sep 06, 2016 at 02:49:08PM +0200, Stanislaw Gruszka wrote:
> > diff --git a/kernel/exit.c b/kernel/exit.c
> > index 2f974ae..a46f96f 100644
> > --- a/kernel/exit.c
> > +++ b/kernel/exit.c
> > @@ -134,7 +134,7 @@ static void __exit_signal(struct task_struct *tsk)
> > sig->inblock += task_io_get_inblock(tsk);
> > sig->oublock += task_io_get_oublock(tsk);
> > task_io_accounting_add(&sig->ioac, &tsk->ioac);
> > - sig->sum_sched_runtime += tsk->se.sum_exec_runtime;
> > + sig->sum_sched_runtime += read_sum_exec_runtime(tsk);
> > sig->nr_threads--;
> > __unhash_process(tsk, group_dead);
> > write_sequnlock(&sig->stats_lock);
>
> If I'm not mistaken, at this point @p is dead, sum_exec_runtime will not
> ever be updated again.
I think at this point find_task_by_vpid() will still return not-null
pointer, hence we can update sum_exec_runtime via:
posix_cpu_{clock_get(),timer_set(),timer_get()} ->
cpu_clock_sample() -> task_sched_runtime() -> update_curr()
if some thread will do cpuclock/cputimer related syscall for
different thread and CPUCLOCK_SCHED clock.
> > diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
> > index 39008d7..a2d753b 100644
> > --- a/kernel/time/posix-cpu-timers.c
> > +++ b/kernel/time/posix-cpu-timers.c
> > @@ -848,7 +848,7 @@ static void check_thread_timers(struct task_struct *tsk,
> > tsk_expires->virt_exp = expires_to_cputime(expires);
> >
> > tsk_expires->sched_exp = check_timers_list(++timers, firing,
> > - tsk->se.sum_exec_runtime);
> > + read_sum_exec_runtime(tsk));
> >
> > /*
> > * Check for the special case thread timers.
>
> @tsk == current and IRQs are disabled, sum_exec_runtime cannot be
> updated.
It still can be updated via syscalls on different thread, same paths
as above.
> > @@ -1115,7 +1115,7 @@ static inline int fastpath_timer_check(struct
> > task_struct *tsk)
> > struct task_cputime task_sample;
> >
> > task_cputime(tsk, &task_sample.utime, &task_sample.stime);
> > - task_sample.sum_exec_runtime = tsk->se.sum_exec_runtime;
> > + task_sample.sum_exec_runtime = read_sum_exec_runtime(tsk);
> > if (task_cputime_expired(&task_sample, &tsk->cputime_expires))
> > return 1;
> > }
>
> Same.
Same :-) But this could be optimized to avoid taking lock if not needed:
if (expires->sum_exec_runtime != 0)
task_sample.sum_exec_runtime = read_sum_exec_runtime(tsk);
Stanislaw
