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From:   Evan Green <evgreen@chromium.org>
Date:   Sun, 7 Aug 2022 22:07:09 -0700
Message-ID: <CAE=gft71vH+P3iAFXC0bLu0M2x2V4uJGWc82Xa+246ECuUdT-w@mail.gmail.com>
Subject: Re: [PATCH v2 03/13] firmware: google: Test spinlock on panic path to
 avoid lockups
To:     "Guilherme G. Piccoli" <gpiccoli@igalia.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, bhe@redhat.com,
        Petr Mladek <pmladek@suse.com>, kexec@lists.infradead.org,
        LKML <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,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Jonathan Corbet <corbet@lwn.net>, d.hatayama@jp.fujitsu.com,
        dave.hansen@linux.intel.com, dyoung@redhat.com,
        feng.tang@intel.com,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        mikelley@microsoft.com, hidehiro.kawai.ez@hitachi.com,
        jgross@suse.com, john.ogness@linutronix.de,
        Kees Cook <keescook@chromium.org>, luto@kernel.org,
        mhiramat@kernel.org, mingo@redhat.com, paulmck@kernel.org,
        peterz@infradead.org, rostedt@goodmis.org,
        senozhatsky@chromium.org, Alan Stern <stern@rowland.harvard.edu>,
        Thomas Gleixner <tglx@linutronix.de>, vgoyal@redhat.com,
        vkuznets@redhat.com, Will Deacon <will@kernel.org>,
        linux-efi@vger.kernel.org, Ard Biesheuvel <ardb@kernel.org>,
        David Gow <davidgow@google.com>,
        Julius Werner <jwerner@chromium.org>
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On Tue, Jul 19, 2022 at 12:55 PM Guilherme G. Piccoli
<gpiccoli@igalia.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@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>

Reviewed-by: Evan Green <evgreen@chromium.org>