linux-kernel - Re: [PATCH v5 6/6] signal: Don't restart fork when signals come in.

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Message-ID: <87600jwi5r.fsf@xmission.com>
Date:   Thu, 09 Aug 2018 12:42:40 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Wen Yang <wen.yang99@....com.cn>, majiang <ma.jiang@....com.cn>
Subject: Re: [PATCH v5 6/6] signal: Don't restart fork when signals come in.

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> On Wed, Aug 8, 2018 at 11:57 PM Eric W. Biederman <ebiederm@...ssion.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.

I just missed the existence of sigdelsetmask when I was putting this
together.

I will fix that and unless someone sees an issue I will queue this up
for linux-next.

Eric