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

Oleg Nesterov
2019-12-17T15:23:45Z

On 12/17, chenqiwu wrote:
>
> But in fact, I think atomic_read()
> can avoid the racy even if both threads exit in parallel, since it is
> an atomic operation forever.

Hmm, not sure I understand. atomic_read() is just READ_ONCE(), it can't be
re-ordered but that is all.

How can it avoid the race if it is called before atomic_dec_and_test() ?

Again, suppose that we have 2 exiting threads and signal->live == 2. With
your patch each thread does atomic_read() before atomic_dec_and_test(),
both threads can observe atomic_read(signal->live) == 2 simply because
the counter was not decremented yet.

Oleg.