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

chenqiwu
2019-12-18T08:08:38Z

On Tue, Dec 17, 2019 at 04:23:33PM +0100, Oleg Nesterov wrote:
> 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.
>

Yeah, I agree your idea.
Now, if there are no further questions, I will resend this as a proper patch for v3.