linux-kernel - Re: [PATCH] signal: remove the wrong signal_pending() check in restore_user

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Message-ID: <20190605090453.GB32406@redhat.com>
Date:   Wed, 5 Jun 2019 11:04:54 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Davidlohr Bueso <dbueso@...e.de>, Jens Axboe <axboe@...nel.dk>,
        Davidlohr Bueso <dave@...olabs.net>, e@...24.org,
        Jason Baron <jbaron@...mai.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-aio@...ck.org, omar.kilani@...il.com,
        Thomas Gleixner <tglx@...utronix.de>,
        stable <stable@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        David Laight <David.Laight@...lab.com>
Subject: Re: [PATCH] signal: remove the wrong signal_pending() check in
 restore_user_sigmask()

On 06/04, Eric W. Biederman wrote:
>
> >> -       restore_user_sigmask(ksig.sigmask, &sigsaved);
> >> -       if (signal_pending(current) && !ret)
> >> +
> >> +       interrupted = signal_pending(current);
> >> +       restore_user_sigmask(ksig.sigmask, &sigsaved, interrupted);
> >> +       if (interrupted && !ret)
> >>                 ret = -ERESTARTNOHAND;
> >
> > are wrong to begin with, and we really should aim for an interface
> > which says "tell me whether you completed the system call, and I'll
> > give you an error return if not".
>
> The pattern you are pointing out is specific to io_pgetevents and it's
> variations.  It does look buggy to me but not for the reason you point
> out, but instead because it does not appear to let a pending signal
> cause io_pgetevents to return early.
>
> I suspect we should fix that and have do_io_getevents return
> -EINTR or -ERESTARTNOHAND like everyone else.

Exactly. It should not even check signal_pending(). It can rely on
wait_event_interruptible_hrtimeout().

> So can we please get this fix in and then look at cleaning up and
> simplifying this code.

Yes ;)

Oleg.