linux-kernel - RE: pselect/etc semantics

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Date:   Thu, 30 May 2019 16:22:35 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'Eric W. Biederman'" <ebiederm@...ssion.com>,
        Oleg Nesterov <oleg@...hat.com>
CC:     Deepa Dinamani <deepa.kernel@...il.com>,
        Al Viro <viro@...IV.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.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>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: pselect/etc semantics

From: Eric W. Biederman
> Sent: 30 May 2019 16:38
> ebiederm@...ssion.com (Eric W. Biederman) writes:
> 
> > Which means I believe we have a semantically valid change in behavior
> > that is causing a regression.
> 
> I haven't made a survey of all of the functions yet but
> fucntions return -ENORESTARTNOHAND will never return -EINTR and are
> immune from this problem.

Eh?
ERESTARTNOHAND just makes the system call restart if there is no
signal handler, EINTR should still be returned if there is a handler.

All the functions that have a temporary signal mask are likely
to be expected to work the same way and thus have the same bugs.

http://pubs.opengroup.org/onlinepubs/9699919799/functions/pselect.html#
isn't overly helpful.
But I think it should return EINTR even if there is no handler unless
SA_RESTART is set:

[EINTR]
    The function was interrupted while blocked waiting for any of the selected descriptors to become ready and before the timeout interval expired.

    If SA_RESTART has been set for the interrupting signal, it is implementation-defined whether the function restarts or returns with [EINTR].

	David

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