Commit 26c4caea authored Jun 27, 2011 by Vasiliy Kulikov Committed by Linus Torvalds Jun 27, 2011

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: Vasiliy Kulikov <segooon@gmail.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 08142579

kernel/taskstats.c

+12 −3

Original line number	Diff line number	Diff line
		@@ -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;
		}

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