linux-kernel - Re: [PATCH v2 03/13] firmware: google: Test spinlock on panic path to avoid lockups

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Date:   Mon, 8 Aug 2022 12:14:30 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     Evan Green <evgreen@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-efi@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Ard Biesheuvel <ardb@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, bhe@...hat.com,
        Petr Mladek <pmladek@...e.com>, kexec@...ts.infradead.org,
        linux-hyperv@...r.kernel.org, netdev@...r.kernel.org,
        x86@...nel.org, kernel-dev@...lia.com, kernel@...ccoli.net,
        halves@...onical.com, fabiomirmar@...il.com,
        alejandro.j.jimenez@...cle.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Jonathan Corbet <corbet@....net>, d.hatayama@...fujitsu.com,
        dave.hansen@...ux.intel.com, dyoung@...hat.com,
        feng.tang@...el.com, mikelley@...rosoft.com,
        hidehiro.kawai.ez@...achi.com, jgross@...e.com,
        john.ogness@...utronix.de, Kees Cook <keescook@...omium.org>,
        luto@...nel.org, mhiramat@...nel.org, mingo@...hat.com,
        paulmck@...nel.org, peterz@...radead.org, rostedt@...dmis.org,
        senozhatsky@...omium.org, Alan Stern <stern@...land.harvard.edu>,
        Thomas Gleixner <tglx@...utronix.de>, vgoyal@...hat.com,
        vkuznets@...hat.com, Will Deacon <will@...nel.org>,
        David Gow <davidgow@...gle.com>,
        Julius Werner <jwerner@...omium.org>
Subject: Re: [PATCH v2 03/13] firmware: google: Test spinlock on panic path to
 avoid lockups

On 08/08/2022 02:07, Evan Green wrote:
> On Tue, Jul 19, 2022 at 12:55 PM Guilherme G. Piccoli
> <gpiccoli@...lia.com> wrote:
>>
>> Currently the gsmi driver registers a panic notifier as well as
>> reboot and die notifiers. The callbacks registered are called in
>> atomic and very limited context - for instance, panic disables
>> preemption and local IRQs, also all secondary CPUs (not executing
>> the panic path) are shutdown.
>>
>> With that said, taking a spinlock in this scenario is a dangerous
>> invitation for lockup scenarios. So, fix that by checking if the
>> spinlock is free to acquire in the panic notifier callback - if not,
>> bail-out and avoid a potential hang.
>>
>> Fixes: 74c5b31c6618 ("driver: Google EFI SMI")
>> Cc: Ard Biesheuvel <ardb@...nel.org>
>> Cc: David Gow <davidgow@...gle.com>
>> Cc: Evan Green <evgreen@...omium.org>
>> Cc: Julius Werner <jwerner@...omium.org>
>> Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
> 
> Reviewed-by: Evan Green <evgreen@...omium.org>

Thanks a bunch Evan!

Ard / Greg, do you think you could get this patch through your -next (or
-fixes) trees? Not sure which tree is the most common for picking GSMI
stuff.

I'm trying to get these fixes merged individually in their trees to not
stall the whole series and increase the burden of re-submitting.
Thanks in advance,


Guilherme