Messages in this thread | | | Date | Tue, 21 Jun 2011 15:49:00 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH v2] taskstats: don't allow duplicate entries in listener mode |
| |
On Thu, 16 Jun 2011 19:55:59 +0400 Vasiliy Kulikov <segoon@openwall.com> wrote:
> Currently a single process may register exit handlers unlimited times. > It may lead to a bloated listeners chain and very slow process terminations. > E.g. after 10KK sent TASKSTATS_CMD_ATTR_REGISTER_CPUMASKs ~300 Mb of > kernel memory is stolen for the handlers chain and "time id" shows 2-7 > seconds instead of normal 0.003. It makes it possible to exhaust all > kernel memory and to eat much of CPU time by triggerring numerous exits > on a single CPU. > > The patch limits the number of times a single process may register > itself on a single CPU to one. > > One little issue is kept unfixed - as taskstats_exit() is called before > exit_files() in do_exit(), the orphaned listener entry (if it was not > explicitly deregistered) is kept until the next someone's exit() and > implicit deregistration in send_cpu_listeners(). So, if a process > registered itself as a listener exits and the next spawned process gets > the same pid, it would inherit taskstats attributes.
ow. That's an unprivileged operation, isn't it?
> > diff --git a/kernel/taskstats.c b/kernel/taskstats.c > index 9ffea36..fc0f220 100644 > --- a/kernel/taskstats.c > +++ b/kernel/taskstats.c > @@ -285,16 +285,18 @@ ret: > static int add_del_listener(pid_t pid, const struct cpumask *mask, int isadd) > { > struct listener_list *listeners; > - struct listener *s, *tmp; > + struct listener *s, *tmp, *s2; > unsigned int cpu; > > if (!cpumask_subset(mask, cpu_possible_mask)) > return -EINVAL; > > + s = NULL; > if (isadd == REGISTER) { > for_each_cpu(cpu, mask) { > - s = kmalloc_node(sizeof(struct listener), GFP_KERNEL, > - cpu_to_node(cpu)); > + if (!s) > + s = kmalloc_node(sizeof(struct listener), > + GFP_KERNEL, cpu_to_node(cpu)); > if (!s) > goto cleanup; > s->pid = pid; > @@ -303,9 +305,16 @@ static int add_del_listener(pid_t pid, const struct cpumask *mask, int isadd) > > listeners = &per_cpu(listener_array, cpu); > down_write(&listeners->sem); > + list_for_each_entry_safe(s2, tmp, &listeners->list, list) { > + if (s2->pid == pid) > + goto next_cpu; > + } > list_add(&s->list, &listeners->list); > + s = NULL; > +next_cpu: > up_write(&listeners->sem); > } > + kfree(s); > return 0; > } >
| |