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Date:   Sun, 7 Aug 2022 12:38:33 -0300
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Subject: Re: [PATCH v2 03/13] firmware: google: Test spinlock on panic path to
 avoid lockups
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To:     kexec@lists.infradead.org, linux-efi@vger.kernel.org,
        Evan Green <evgreen@chromium.org>
Cc:     pmladek@suse.com, bhe@redhat.com, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org,
        netdev@vger.kernel.org, x86@kernel.org, kernel-dev@igalia.com,
        kernel@gpiccoli.net, halves@canonical.com, fabiomirmar@gmail.com,
        alejandro.j.jimenez@oracle.com, andriy.shevchenko@linux.intel.com,
        arnd@arndb.de, bp@alien8.de, corbet@lwn.net,
        d.hatayama@jp.fujitsu.com, dave.hansen@linux.intel.com,
        dyoung@redhat.com, feng.tang@intel.com, gregkh@linuxfoundation.org,
        mikelley@microsoft.com, hidehiro.kawai.ez@hitachi.com,
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        senozhatsky@chromium.org, stern@rowland.harvard.edu,
        tglx@linutronix.de, vgoyal@redhat.com, vkuznets@redhat.com,
        will@kernel.org, Ard Biesheuvel <ardb@kernel.org>,
        Julius Werner <jwerner@chromium.org>,
        David Gow <davidgow@google.com>
References: <20220719195325.402745-1-gpiccoli@igalia.com>
 <20220719195325.402745-4-gpiccoli@igalia.com>
From:   "Guilherme G. Piccoli" <gpiccoli@igalia.com>
In-Reply-To: <20220719195325.402745-4-gpiccoli@igalia.com>
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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@kernel.org>
> Cc: David Gow <davidgow@google.com>
> Cc: Evan Green <evgreen@chromium.org>
> Cc: Julius Werner <jwerner@chromium.org>
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.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