linux-kernel - Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

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Message-ID: <20170526215518.GB40877@dtor-ws>
Date:   Fri, 26 May 2017 14:55:18 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Fuzzey, Martin" <mfuzzey@...keon.com>,
        Andy Lutomirski <luto@...nel.org>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        Linux API <linux-api@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Daniel Wagner <wagi@...om.org>,
        David Woodhouse <dwmw2@...radead.org>,
        jewalt@...innovations.com, rafal@...ecki.pl,
        Arend Van Spriel <arend.vanspriel@...adcom.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Li, Yi" <yi1.li@...ux.intel.com>, atull@...nsource.altera.com,
        Moritz Fischer <moritz.fischer@...us.com>,
        Petr Mladek <pmladek@...e.com>,
        Johannes Berg <johannes.berg@...el.com>,
        Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
        Luca Coelho <luciano.coelho@...el.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        David Howells <dhowells@...hat.com>,
        Peter Jones <pjones@...hat.com>,
        Hans de G oede <hdegoede@...hat.com>,
        Alan Cox <alan@...ux.intel.com>, Ted Ts'o <tytso@....edu>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on
 fallback

On Fri, May 26, 2017 at 02:32:31PM -0700, Luis R. Rodriguez wrote:
> On Fri, May 26, 2017 at 2:26 PM, Dmitry Torokhov
> <dmitry.torokhov@...il.com> wrote:
> > On Fri, May 26, 2017 at 12:46 PM, Luis R. Rodriguez <mcgrof@...nel.org> wrote:
> >> On Fri, May 26, 2017 at 06:09:29AM -0500, Eric W. Biederman wrote:
> >>> "Fuzzey, Martin" <mfuzzey@...keon.com> writes:
> >>> >>>> Maybe SIGCHLD shouldn't interrupt firmware loading?
> >>> >
> >>> > I don't think there's a way of doing that without disabling all
> >>> > signals (ie using the non interruptible wait variants).
> >>> > It used to be that way (which is why I only ran into this after
> >>> > updating from an ancient 3.16 kernel to a slightly less ancient 4.4)
> >>> > But there are valid reasons for wanting to be able to interrupt
> >>> > firmware loading (like being able to kill the userspace helper)
> >>>
> >>> Perhaps simply using a killable wait and not a fully interruptible
> >>> wait would be better?
> >>
> >> What do you mean by a killable wait BTW?
> >
> > https://lwn.net/Articles/288056/
> >
> > I think only interrupting firmware loading with fatal signals would
> > make a lot of sense.
> >
> >>
> >> ret = swait_event_interruptible_timeout() is being used right now.
> >
> > It looks like we are missing swait_event_killable*(), but I do not
> > think it would be hard to add.
> 
> What should we do for stable ? Is this a *stable* issue ?

I think it is, as you have users complaining about behavior. I do not
think we need to make their lives harder than needed by requiring
handling signals.

I do not see why we could not introduce wait_event_killable_timeout()
and swait_event_killable_timeout() into -stables.

Thanks.

-- 
Dmitry