Re: [PATCH v2] kernel/exit: do panic earlier to get coredump if global init task exit

Oleg Nesterov
2019-12-17T14:25:28Z

On 12/17, chenqiwu wrote:
>
> @@ -728,6 +724,15 @@ void __noreturn do_exit(long code)
> panic("Attempted to kill the idle task!");
>
> /*
> + * If all threads of global init have exited, do panic imeddiately
> + * to get the coredump to find any clue for init task in userspace.
> + */
> + if (unlikely(is_global_init(tsk) &&
> + (atomic_read(&tsk->signal->live) == 1)))

Well, I guess this will work in practice, but in theory this is racy.

Suppose that signal->live == 2 and both threads exit in parallel. They
both can see tsk->signal->live == 2 before atomic_dec_and_test().

If you are fine with this race I won't object, but please add a comment.

But why can't you simply do

--- x/kernel/exit.c
+++ x/kernel/exit.c
@@ -786,6 +786,8 @@ void __noreturn do_exit(long code)
acct_update_integrals(tsk);
group_dead = atomic_dec_and_test(&tsk->signal->live);
if (group_dead) {
+ if (unlikely(is_global_init(tsk)
+ panic(...);
#ifdef CONFIG_POSIX_TIMERS
hrtimer_cancel(&tsk->signal->real_timer);
exit_itimers(tsk->signal);

?

Oleg.