On 11/06, Nam Cao wrote:
>
> @@ -534,6 +517,23 @@ static int do_task_stat(struct seq_file *m, struct
> pid_namespace *ns,
> ppid = task_tgid_nr_ns(task->real_parent, ns);
> pgid = task_pgrp_nr_ns(task, ns);
>
> + /*
> + * esp and eip are intentionally zeroed out. There is no
> + * non-racy way to read them without freezing the task.
> + * Programs that need reliable values can use ptrace(2).
OK,
but then:
> + * The only exception is if the task is core dumping because
> + * a program is not able to use ptrace(2) in that case. It is
> + * safe because the task has stopped executing permanently.
> + */
> + if (permitted && task->signal->core_state) {
> + if (try_get_task_stack(task)) {
> + eip = KSTK_EIP(task);
> + esp = KSTK_ESP(task);
> + put_task_stack(task);
How can the task->signal->core_state check help ?
Suppose we have a task T1 with T1-pid == 100 and you read /proc/100/stat.
It is possible that the T1's sub-thread T2 starts the coredumping and sets
signal->core_state != NULL.
But read(/proc/100/stat) can run before T1 gets SIGKILL from T2 and enters
the kernel mode?
Oleg.
