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    Subject[PATCH 6.0 563/862] firmware: google: Test spinlock on panic path to avoid lockups
    Date
    From: Guilherme G. Piccoli <gpiccoli@igalia.com>

    [ Upstream commit 3e081438b8e639cc76ef1a5ce0c1bd8a154082c7 ]

    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: Andrew Morton <akpm@linux-foundation.org>
    Cc: Ard Biesheuvel <ardb@kernel.org>
    Cc: David Gow <davidgow@google.com>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: Julius Werner <jwerner@chromium.org>
    Cc: Petr Mladek <pmladek@suse.com>
    Reviewed-by: Evan Green <evgreen@chromium.org>
    Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
    Link: https://lore.kernel.org/r/20220909200755.189679-1-gpiccoli@igalia.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/firmware/google/gsmi.c | 9 +++++++++
    1 file changed, 9 insertions(+)

    diff --git a/drivers/firmware/google/gsmi.c b/drivers/firmware/google/gsmi.c
    index adaa492c3d2d..4e2575dfeb90 100644
    --- a/drivers/firmware/google/gsmi.c
    +++ b/drivers/firmware/google/gsmi.c
    @@ -681,6 +681,15 @@ static struct notifier_block gsmi_die_notifier = {
    static int gsmi_panic_callback(struct notifier_block *nb,
    unsigned long reason, void *arg)
    {
    +
    + /*
    + * Panic callbacks are executed with all other CPUs stopped,
    + * so we must not attempt to spin waiting for gsmi_dev.lock
    + * to be released.
    + */
    + if (spin_is_locked(&gsmi_dev.lock))
    + return NOTIFY_DONE;
    +
    gsmi_shutdown_reason(GSMI_SHUTDOWN_PANIC);
    return NOTIFY_DONE;
    }
    --
    2.35.1


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