linux-kernel - Re: [PATCH v7 03/20] reboot: Print error message if restart handler has duplicated priority

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAJZ5v0iA6St_J5C6+Efygu25g9g-_tLBPc0qQoHbFqfrdT6azQ@mail.gmail.com>
Date:   Wed, 20 Apr 2022 19:36:23 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Guo Ren <guoren@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Joshua Thompson <funaho@...ai.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Sebastian Reichel <sre@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>, Pavel Machek <pavel@....cz>,
        Lee Jones <lee.jones@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-csky@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-m68k@...ts.linux-m68k.org,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        linux-parisc@...r.kernel.org, linux-riscv@...ts.infradead.org,
        Linux-sh list <linux-sh@...r.kernel.org>,
        xen-devel@...ts.xenproject.org,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v7 03/20] reboot: Print error message if restart handler
 has duplicated priority

On Mon, Apr 18, 2022 at 3:29 AM Dmitry Osipenko
<dmitry.osipenko@...labora.com> wrote:
>
> On 4/14/22 14:19, Rafael J. Wysocki wrote:
> > On Thu, Apr 14, 2022 at 12:24 AM Dmitry Osipenko
> > <dmitry.osipenko@...labora.com> wrote:
> >>
> >> On 4/13/22 21:48, Rafael J. Wysocki wrote:
> >>> On Tue, Apr 12, 2022 at 1:39 AM Dmitry Osipenko
> >>> <dmitry.osipenko@...labora.com> wrote:
> >>>>
> >>>> Add sanity check which ensures that there are no two restart handlers
> >>>> registered using the same priority. This requirement will become mandatory
> >>>> once all drivers will be converted to the new API and such errors will be
> >>>> fixed.
> >>>>
> >>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> >>>
> >>> The first two patches in the series are fine with me and there's only
> >>> one minor nit regarding this one (below).
> >>>
> >>>> ---
> >>>>  kernel/reboot.c | 15 +++++++++++++++
> >>>>  1 file changed, 15 insertions(+)
> >>>>
> >>>> diff --git a/kernel/reboot.c b/kernel/reboot.c
> >>>> index ed4e6dfb7d44..acdae4e95061 100644
> >>>> --- a/kernel/reboot.c
> >>>> +++ b/kernel/reboot.c
> >>>> @@ -182,6 +182,21 @@ static ATOMIC_NOTIFIER_HEAD(restart_handler_list);
> >>>>   */
> >>>>  int register_restart_handler(struct notifier_block *nb)
> >>>>  {
> >>>> +       int ret;
> >>>> +
> >>>> +       ret = atomic_notifier_chain_register_unique_prio(&restart_handler_list, nb);
> >>>> +       if (ret != -EBUSY)
> >>>> +               return ret;
> >>>> +
> >>>> +       /*
> >>>> +        * Handler must have unique priority. Otherwise call order is
> >>>> +        * determined by registration order, which is unreliable.
> >>>> +        *
> >>>> +        * This requirement will become mandatory once all drivers
> >>>> +        * will be converted to use new sys-off API.
> >>>> +        */
> >>>> +       pr_err("failed to register restart handler using unique priority\n");
> >>>
> >>> I would use pr_info() here, because this is not a substantial error AFAICS.
> >>
> >> It's indeed not a substantial error so far, but it will become
> >> substantial later on once only unique priorities will be allowed. The
> >> pr_warn() could be a good compromise here, pr_info() is too mild, IMO.
> >
> > Well, I'm still unconvinced about requiring all of the users of this
> > interface to use unique priorities.
> >
> > Arguably, there are some of them who don't really care about the
> > ordering, so could there be an option for them to specify the lack of
> > care by, say, passing 0 as the priority that would be regarded as a
> > special case?
> >
> > IOW, if you pass 0, you'll be run along the others who've also passed
> > 0, but if you pass anything different from 0, it must be unique.  What
> > do you think?
>
> There are indeed cases where ordering is unimportant. Like a case of
> PMIC and watchdog restart handlers for example, both handlers will
> produce equal effect from a user's perspective. Perhaps indeed it's more
> practical to have at least one shared level.
>
> In this patchset the level 0 is specified as an alias to the default
> level 128. If one user registers handler using unique level 128 and the
> other user uses non-unique level 0, then we have ambiguity.
>
> One potential option is to make the whole default level 128 non-unique.
> This will allow users to not care about the uniqueness by default like
> they always did it previously, but it will hide potential problems for
> users who actually need unique level and don't know about it yet due to
> a lucky registration ordering that they have today. Are you okay with
> this option?

Yes, I am.