linux-kernel - Re: pselect/etc semantics (Was: [PATCH v2] signal: Adjust error codes according to restore_user

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Date:   Thu, 30 May 2019 20:37:29 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Deepa Dinamani <deepa.kernel@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>, dbueso@...e.de,
        Jens Axboe <axboe@...nel.dk>,
        Davidlohr Bueso <dave@...olabs.net>, e@...24.org,
        Jason Baron <jbaron@...mai.com>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        linux-aio <linux-aio@...ck.org>, omar.kilani@...il.com,
        Thomas Gleixner <tglx@...utronix.de>,
        "# 3.4.x" <stable@...r.kernel.org>
Subject: Re: pselect/etc semantics (Was: [PATCH v2] signal: Adjust error codes
 according to restore_user_sigmask())

On Thu, May 30, 2019 at 4:41 PM Oleg Nesterov <oleg@...hat.com> wrote:
> On 05/30, Arnd Bergmann wrote:
> Plus every file touched by this patch asks for more cleanups. Say, do_poll()
> should return -ERESTARTNOHAND, not -EINTR, after that we can remove the ugly
> EINTR->ERESTARTNOHAND in its callers. And more.
>
> > For the stable
> > kernels, I think we want just the addition of the 'bool interrupted' argument
> > to restore_user_sigmask()
>
> or simply revert this patch. I will check if this is possible today... At first
> glance 854a6ed56839a40f6 fixed another bug by accident, do_pselect() did
> "ret == -ERESTARTNOHAND" after "ret = poll_select_copy_remaining()" which can
> turn ERESTARTNOHAND into EINTR, but this is simple. I'll check tomorrow.

Right, there were several differences between the system calls
that Deepa's original change got rid of. I don't know if any ones besides
the do_pselect() return code can be observed in practice.

> > > -       ret = set_user_sigmask(ksig.sigmask, &ksigmask, &sigsaved, ksig.sigsetsize);
> > > +       ret = set_xxx(ksig.sigmask, ksig.sigsetsize);
> > >         if (ret)
> > >                 return ret;
> > >
> > >         ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &ts : NULL);
> > > -       restore_user_sigmask(ksig.sigmask, &sigsaved);
> > > -       if (signal_pending(current) && !ret)
> > > +
> > > +       interrupted = signal_pending(current);
> > > +       update_xxx(interrupted);
> >
> > Maybe name this
> >
> >            restore_saved_sigmask_if(!interrupted);
>
> Yes, I thought about restore_if(), but to me
>
>                 restore_saved_sigmask_if(ret != -EINTR);
>
> doesn't look readable... May be
>
>                 restore_saved_sigmask_unless(ret == -EINTR);
>
> ? but actually I agree with any naming.

Yes, restore_saved_sigmask_unless() probably better.

> > With some of the recent discussions about compat syscall handling,
> > I now think that we want to just fold set_compat_user_sigmask()
> > into set_user_sigmask()
>
> agreed, and I thought about this too. But again, I'd prefer to do this
> and other cleanups later, on top of this patch.

Ok, fair enough. I don't care much about the order as long as the
regression fix comes first.

     Arnd