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Re: [PATCH v4 06/25] reboot: Warn if unregister_restart_handler() fails
- To: Dmitry Osipenko <digetx@xxxxxxxxx>
- From: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
- Date: Fri, 10 Dec 2021 20:08:21 +0100
- Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>, Thierry Reding <thierry.reding@xxxxxxxxx>, Jonathan Hunter <jonathanh@xxxxxxxxxx>, Russell King <linux@xxxxxxxxxxxxxxx>, Catalin Marinas <catalin.marinas@xxxxxxx>, Will Deacon <will@xxxxxxxxxx>, Guo Ren <guoren@xxxxxxxxxx>, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>, Greg Ungerer <gerg@xxxxxxxxxxxxxx>, Joshua Thompson <funaho@xxxxxxxxx>, Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>, Sebastian Reichel <sre@xxxxxxxxxx>, Linus Walleij <linus.walleij@xxxxxxxxxx>, Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>, Greentime Hu <green.hu@xxxxxxxxx>, Vincent Chen <deanbo422@xxxxxxxxx>, "James E.J. Bottomley" <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>, Helge Deller <deller@xxxxxx>, Michael Ellerman <mpe@xxxxxxxxxxxxxx>, Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>, Paul Mackerras <paulus@xxxxxxxxx>, Paul Walmsley <paul.walmsley@xxxxxxxxxx>, Palmer Dabbelt <palmer@xxxxxxxxxxx>, Albert Ou <aou@xxxxxxxxxxxxxxxxx>, Yoshinori Sato <ysato@xxxxxxxxxxxxxxxxxxxx>, Rich Felker <dalias@xxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, "the arch/x86 maintainers" <x86@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Len Brown <lenb@xxxxxxxxxx>, Santosh Shilimkar <ssantosh@xxxxxxxxxx>, Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxxxxx>, Liam Girdwood <lgirdwood@xxxxxxxxx>, Mark Brown <broonie@xxxxxxxxxx>, Pavel Machek <pavel@xxxxxx>, Lee Jones <lee.jones@xxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Guenter Roeck <linux@xxxxxxxxxxxx>, Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>, Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>, Ulf Hansson <ulf.hansson@xxxxxxxxxx>, alankao@xxxxxxxxxxxxx, "K . C . Kuen-Chern Lin" <kclin@xxxxxxxxxxxxx>, Linux ARM <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, linux-csky@xxxxxxxxxxxxxxx, linux-ia64@xxxxxxxxxxxxxxx, linux-m68k@xxxxxxxxxxxxxxxxxxxx, linux-mips@xxxxxxxxxxxxxxx, linux-parisc@xxxxxxxxxxxxxxx, linuxppc-dev <linuxppc-dev@xxxxxxxxxxxxxxxx>, linux-riscv@xxxxxxxxxxxxxxxxxxx, Linux-sh list <linux-sh@xxxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, ACPI Devel Maling List <linux-acpi@xxxxxxxxxxxxxxx>, Linux PM <linux-pm@xxxxxxxxxxxxxxx>, linux-tegra <linux-tegra@xxxxxxxxxxxxxxx>
- Delivery-date: Fri, 10 Dec 2021 19:08:47 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Fri, Dec 10, 2021 at 7:54 PM Dmitry Osipenko <digetx@xxxxxxxxx> wrote:
>
> 10.12.2021 21:32, Rafael J. Wysocki пишет:
> > On Fri, Nov 26, 2021 at 7:02 PM Dmitry Osipenko <digetx@xxxxxxxxx> wrote:
> >>
> >> Emit warning if unregister_restart_handler() fails since it never should
> >> fail. This will ease further API development by catching mistakes early.
> >>
> >> Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> >> ---
> >> kernel/reboot.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/kernel/reboot.c b/kernel/reboot.c
> >> index e6659ae329f1..f0e7b9c13f6b 100644
> >> --- a/kernel/reboot.c
> >> +++ b/kernel/reboot.c
> >> @@ -210,7 +210,7 @@ EXPORT_SYMBOL(register_restart_handler);
> >> */
> >> int unregister_restart_handler(struct notifier_block *nb)
> >> {
> >> - return atomic_notifier_chain_unregister(&restart_handler_list, nb);
> >> + return
> >> WARN_ON(atomic_notifier_chain_unregister(&restart_handler_list, nb));
> >
> > The only reason why it can fail is if the object pointed to by nb is
> > not in the chain.
>
> I had exactly this case where object wasn't in the chain due to a bug
> and this warning was very helpful.
During the development. In production it would be rather annoying.
> > Why WARN() about this? And what about systems with
> > panic_on_warn set?
>
> That warning condition will never happen normally, only when something
> is seriously wrong.
>
> Those systems with panic_on_warn will get what was they asked for.
They may not be asking for panicking on bugs in the reboot notifier
code, though. That's what your change is making them panic on.
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