Messages in this thread | | | Date | Wed, 7 Sep 2016 09:01:24 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v3] sched/cputime: Protect some other sum_exec_runtime reads on 32 bit cpus |
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On Wed, Sep 07, 2016 at 08:38:27AM +0200, Stanislaw Gruszka wrote: > 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.
Ah, ok. I always forget how the exit path works..
> > > 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.
Yep, realized that over-night.
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