Messages in this thread | | | Date | Mon, 16 Mar 2009 10:07:54 +0530 | From | Bharata B Rao <> | Subject | Re: [RFC PATCH -tip] cpuacct: per-cgroup utime/stime statistics - v2 |
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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@linux.vnet.ibm.com> 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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