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Re: signals: Bug or manpage inconsistency?

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On 05/30, Linus Torvalds wrote:
>
> On Tue, May 30, 2017 at 10:04 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > I can't comment, I never tried to understand the rationality behind the current
> > behaviour. But at least the sending path should never drop a blocked SIG_DFL
> > signal, there is no other way to ensure you won't miss a signal during exec.
>
> Note that both SIG_DFL _and_ SIG_IGN are possible after exec,

Yes, if it was already ignored before exec. But ignoring the compatibility the
only important case is when it is SIG_DFL because of flush_signal_handlers().

> SIG_IGN doesn't mean "ignore signal forever". It means "ignore signals
> right now", and I think that our current signal blocking semantics are
> likely the correct ones,

I am not saying it is incorrect, but I agree with Thomas in that this
sigismember(t->blocked) in sig_ignored() doesn't look really nice.

> exactly because it means "when you start
> blocking signals, the kernel will not drop them".

if the process is singe-threaded or the signal is private, or it is blocked
by all threads. Otherwise it will wakeup another thread for no reason, the
signal will be dropped in get_signal().

And again, this doesn't look consistent with do_sigaction(). It even has a
comment which explains that we want to flush the ignored signals, blocked
or not.

Nevermind, I am not trying to argue, and

> So again, I really wouldn't want to change existing semantics unless
> there is a big real reason for it. Our current semantics are not
> wrong.

I certainly agree.

Oleg.

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Thread

signals: Bug or manpage inconsistency? Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 15:30 +0200
  Re: signals: Bug or manpage inconsistency? Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 18:20 +0200
    Re: signals: Bug or manpage inconsistency? Oleg Nesterov <oleg@redhat.com> - 2017-05-30 19:10 +0200
      Re: signals: Bug or manpage inconsistency? Linus Torvalds <torvalds@linux-foundation.org> - 2017-05-30 19:20 +0200
        Re: signals: Bug or manpage inconsistency? Oleg Nesterov <oleg@redhat.com> - 2017-05-30 21:20 +0200
        Re: signals: Bug or manpage inconsistency? Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:00 +0200
          Re: signals: Bug or manpage inconsistency? ebiederm@xmission.com (Eric W. Biederman) - 2017-05-31 03:00 +0200
            Re: signals: Bug or manpage inconsistency? ebiederm@xmission.com (Eric W. Biederman) - 2017-05-31 03:20 +0200
  Re: signals: Bug or manpage inconsistency? Linus Torvalds <torvalds@linux-foundation.org> - 2017-05-30 19:10 +0200
    Re: signals: Bug or manpage inconsistency? Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 21:40 +0200
      Re: signals: Bug or manpage inconsistency? Linus Torvalds <torvalds@linux-foundation.org> - 2017-05-30 22:00 +0200
        Re: signals: Bug or manpage inconsistency? Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:10 +0200
  Re: signals: Bug or manpage inconsistency? "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2017-05-31 09:00 +0200
  Re: signals: Bug or manpage inconsistency? ebiederm@xmission.com (Eric W. Biederman) - 2017-06-01 09:10 +0200

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