On Mon, Mar 16, 2009 at 10:35:17AM +0900, KAMEZAWA Hiroyuki wrote:
> On Thu, 12 Mar 2009 16:39:24 +0530
> Bharata B Rao <bharata@xxxxxxxxxxxxxxxxxx> wrote:
>
> > #ifdef CONFIG_CGROUP_CPUACCT
> > static void cpuacct_charge(struct task_struct *tsk, u64 cputime);
> > +static void cpuacct_update_stats(struct task_struct *tsk,
> > + enum cpuacct_stat_index idx, cputime_t val);
> > #else
> > static inline void cpuacct_charge(struct task_struct *tsk, u64 cputime) {}
> > +static void cpuacct_update_stats(struct task_struct *tsk,
> > + enum cpuacct_stat_index idx, cputime_t val) {}
> > #endif
> "static inline"
> if no "inline", the complier will show warning as
> "this function is defined but not used.."
Ok.
> >
> > +/*
> > + * Account the system/user time to the task's accounting group.
> > + */
> > +static void cpuacct_update_stats(struct task_struct *tsk,
> > + enum cpuacct_stat_index idx, cputime_t val)
> > +{
> > + struct cpuacct *ca;
> > +
> > + if (unlikely(!cpuacct_subsys.active))
> > + return;
> > +
> > + ca = task_ca(tsk);
> > +
> > + do {
> > + percpu_counter_add(&ca->cpustat[idx], val);
> > + ca = ca->parent;
> > + } while (ca);
> > +}
> > +
>
> IIUC, to make sure accessing "ca" to be safe, we need some condition.
> (task_lock() or some other.....
task_lock() protects tsk->cgroups->subsys[]. So can we hold task_lock()
to protect this walk ? But we do this cpuacct hierarchy walk for the
current task here. So can a current task's ca or ca's parents disappear
from under us ?
Regards,
Bharata.
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