Re: [PATCH] multipathd: fix inverted signal blocking logic

[Martin Wilck <mwilck@suse.com>]

Hello Bart,

On Mon, 2018-03-05 at 16:27 +0000, Bart Van Assche wrote:
> On Sat, 2018-03-03 at 01:31 +0100, Martin Wilck wrote:
> > So, there's no reason not to block them, right? Is it expected
> > behavior
> > that a user running 'kill -USR2 $(pidof multipathd)' terminates the
> > process? Why do you think these signals should interrupt ppoll()
> > although the uxlsnr can't can't handle them? Isn't it sufficient
> > that
> > they're handled by the threads that are meant to do that?
> 
> Blocking all signals except the ones for which we installed a handler
> sounds
> weird to me. I think users expect daemons to process signals instead
> of
> blocking all but a specific set of signals. This is a rather
> philosophical
> argument and not an argument of which I think that it is strong
> enough to
> prevent this patch of being integrated in the upstream multipath-
> tools
> repository.

Thank you. Meanwhile, I found that this patch requires a change in the
"marginal paths" code. I'll post an official patch as update.

Regarding the philosophical discussion, may I remind you of your own
words from 534ec4c?

    The POSIX standard mentions that the only way to guarantee that
    signals are delivered to a specific thread is:
     * Block all signals before the first pthread_create() call.
     * Unblock signals from the thread that should receive signals.

If we unblock signals with a default disposition of "Term" for which we
have no handler, stray signals caught would terminate multipathd. I
don't think that's what we want. Of course we must react on
SIGINT/SIGTERM/SIGHUP in the way the user expects us to, but
terminating on other signals would be wrong.

Let's see if others have to say anything about this.

Martin

-- 
Dr. Martin Wilck <mwilck@suse.com>, Tel. +49 (0)911 74053 2107
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)

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