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 12:38:33 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     kexec@...ts.infradead.org, linux-efi@...r.kernel.org,
        Evan Green <evgreen@...omium.org>
Cc:     pmladek@...e.com, bhe@...hat.com, akpm@...ux-foundation.org,
        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, andriy.shevchenko@...ux.intel.com,
        arnd@...db.de, bp@...en8.de, corbet@....net,
        d.hatayama@...fujitsu.com, dave.hansen@...ux.intel.com,
        dyoung@...hat.com, feng.tang@...el.com, gregkh@...uxfoundation.org,
        mikelley@...rosoft.com, hidehiro.kawai.ez@...achi.com,
        jgross@...e.com, john.ogness@...utronix.de, keescook@...omium.org,
        luto@...nel.org, mhiramat@...nel.org, mingo@...hat.com,
        paulmck@...nel.org, peterz@...radead.org, rostedt@...dmis.org,
        senozhatsky@...omium.org, stern@...land.harvard.edu,
        tglx@...utronix.de, vgoyal@...hat.com, vkuznets@...hat.com,
        will@...nel.org, Ard Biesheuvel <ardb@...nel.org>,
        Julius Werner <jwerner@...omium.org>,
        David Gow <davidgow@...gle.com>
Subject: Re: [PATCH v2 03/13] firmware: google: Test spinlock on panic path to
 avoid lockups

On 19/07/2022 16:53, Guilherme G. Piccoli 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>
> 
> ---
> 
> V2:
> - do not use spin_trylock anymore, to avoid messing with
> non-panic paths; now we just check the spinlock state in
> the panic notifier before taking it. Thanks Evan for the
> review/idea!
> 
>  drivers/firmware/google/gsmi.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> [...]

Hi Evan, do you think this one is good now, based on your previous review?

Appreciate any feedback!
Cheers,


Guilherme