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Commit 26c4caea authored by Vasiliy Kulikov's avatar Vasiliy Kulikov Committed by Linus Torvalds
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taskstats: don't allow duplicate entries in listener mode 



Currently a single process may register exit handlers unlimited times.
It may lead to a bloated listeners chain and very slow process
terminations.

Eg 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.

Signed-off-by: default avatarVasiliy Kulikov <segooon@gmail.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 08142579

kernel/taskstats.c

+12 −3
Original line number Diff line number Diff line
@@ -285,16 +285,18 @@ static void fill_tgid_exit(struct task_struct *tsk) 
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;

	}