linux-kernel - Re: [RFC PATCH 1/5] signal: Teach sigsuspend to use set_user

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Message-ID: <20190612153756.GD3276@redhat.com>
Date:   Wed, 12 Jun 2019 17:37:57 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     David Laight <David.Laight@...LAB.COM>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "arnd@...db.de" <arnd@...db.de>, "dbueso@...e.de" <dbueso@...e.de>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "dave@...olabs.net" <dave@...olabs.net>,
        "e@...24.org" <e@...24.org>,
        "jbaron@...mai.com" <jbaron@...mai.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-aio@...ck.org" <linux-aio@...ck.org>,
        "omar.kilani@...il.com" <omar.kilani@...il.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        Al Viro <viro@...IV.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: [RFC PATCH 1/5] signal: Teach sigsuspend to use set_user_sigmask

On 06/12, Eric W. Biederman wrote:
> David Laight <David.Laight@...LAB.COM> writes:
>
> > From: Oleg Nesterov
> >> Sent: 12 June 2019 14:46
> >> On 06/11, David Laight wrote:
> >> >
> >> > If I have an application that has a loop with a pselect call that
> >> > enables SIGINT (without a handler) and, for whatever reason,
> >> > one of the fd is always 'ready' then I'd expect a SIGINT
> >> > (from ^C) to terminate the program.
>
> I think this gets into a quality of implementation.
>
> I suspect that set_user_sigmask should do:
> if (signal_pending())
> 	return -ERESTARNOSIGHAND; /* -EINTR that restarts if nothing was pending */
>
> Which should be safe as nothing has blocked yet to consume any of the
> timeouts, and it should ensure that none of the routines miss a signal.

Why? I don't think this makes any sense.

Perhaps we could do this _after_ set_current_blocked() for the case when
the already pending SIGINT was unblocked but a) I am not sure this would
be really better and b) I think it is too late to change this.

Oleg.