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

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Date:   Wed, 12 Jun 2019 08:39:53 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Oleg Nesterov' <oleg@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
CC:     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

From: Oleg Nesterov [mailto:oleg@...hat.com]
> Sent: 11 June 2019 19:56
> On 06/10, Eric W. Biederman wrote:
> >
> > Personally I don't think anyone sane would intentionally depend on this
> > and I don't think there is a sufficiently reliable way to depend on this
> > by accident that people would actually be depending on it.
> 
> Agreed.
> 
> As I said I like these changes and I see nothing wrong. To me they fix the
> current behaviour, or at least make it more consistent.
> 
> But perhaps this should be documented in the changelog? To make it clear
> that this change was intentional.

What happens if you run the test program I posted yesterday after the changes?

It looks like pselect() and epoll_pwait() operated completely differently.
pselect() would always calls the signal handlers.
epoll_pwait() only calls them when EINTR is returned.
So changing epoll_pwait() and pselect() to work the same way
is bound to break some applications.

	David

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