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

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Date:   Sun, 7 Aug 2022 22:07:09 -0700
From:   Evan Green <evgreen@...omium.org>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, bhe@...hat.com,
        Petr Mladek <pmladek@...e.com>, kexec@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.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,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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>,
        linux-efi@...r.kernel.org, Ard Biesheuvel <ardb@...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 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>