On Wed, May 29, 2019 at 9:12 AM Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>
> Al, Linus, Eric, please help.
>
> The previous discussion was very confusing, we simply can not understand each
> other.
>
> To me everything looks very simple and clear, but perhaps I missed something
> obvious? Please correct me.
>
> I think that the following code is correct
>
> int interrupted = 0;
>
> void sigint_handler(int sig)
> {
> interrupted = 1;
> }
>
> int main(void)
> {
> sigset_t sigint, empty;
>
> sigemptyset(&sigint);
> sigaddset(&sigint, SIGINT);
> sigprocmask(SIG_BLOCK, &sigint, NULL);
>
> signal(SIGINT, sigint_handler);
>
> sigemptyset(&empty); // so pselect() unblocks SIGINT
>
> ret = pselect(..., &empty);
>
> if (ret >= 0) // sucess or timeout
> assert(!interrupted);
>
> if (interrupted)
> assert(ret == -EINTR);
> }
>
> IOW, if pselect(sigmask) temporary unblocks SIGINT according to sigmask, this
> signal should not be delivered if a ready fd was found or timeout. The signal
> handle should only run if ret == -EINTR.
I do not think we discussed this part earlier. But, if this is true
then this is what is wrong as part of 854a6ed56839a. I missed that
before.
> (pselect() can be interrupted by any other signal which has a handler. In this
> case the handler can be called even if ret >= 0. This is correct, I fail to
> understand why some people think this is wrong, and in any case we simply can't
> avoid this).
This patch is wrong because I did not know that it was ok to deliver a
signal and not set the errno before. I also admitted to this. And
proposed another way to revert the patch.:
https://lore.kernel.org/lkml/CABeXuvouBzZuNarmNcd9JgZgvonL1N_p21gat=O_x0-1hMx=6A@xxxxxxxxxxxxxx/
-Deepa
