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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 9 Aug 2018 10:15:43 -0700
Message-ID: <CA+55aFyuJHWW__t_Pq+AqVhiGOVnbd7wKKdX8AH8YUzfzb0=YA@mail.gmail.com>
Subject: Re: [PATCH v5 6/6] signal: Don't restart fork when signals come in.
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Oleg Nesterov <oleg@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Wen Yang <wen.yang99@zte.com.cn>, majiang <ma.jiang@zte.com.cn>
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On Wed, Aug 8, 2018 at 11:57 PM Eric W. Biederman <ebiederm@xmission.com> wrote:
>
> The code was being overly pesimistic.

Pessimistic.

> +       if (type > PIDTYPE_TGID) {
> +               struct multiprocess_signals *delayed;
> +               hlist_for_each_entry(delayed, &t->signal->multiprocess, node) {
> +                       sigset_t *signal = &delayed->signal;
> +                       /* Can't queue both a stop and a continue signal */
> +                       if (sig == SIGCONT) {
> +                               sigset_t flush;
> +                               siginitset(&flush, SIG_KERNEL_STOP_MASK);
> +                               sigandnsets(signal, signal, &flush);

This looks odd and unnecessary.

Why isn't this just a

        sigdelsetmask(signal, SIG_KERNEL_STOP_MASK);

since all of the traditional stop bits should be in the low mask.

I see that we apparently have this stupid pattern elsewhere too, and
it looks like it's because we stupidly say "are the RT signals in the
non-legacy set", when that definitely cannot be the case for the (very
much legacy) tty flow control signals.

                 Linus