firmware: google: test spinlock on panic path to avoid lockups
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. Link: https://lkml.kernel.org/r/20220909200755.189679-1-gpiccoli@igalia.com Fixes: 74c5b31c6618 ("driver: Google EFI SMI") Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com> Reviewed-by: Evan Green <evgreen@chromium.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> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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@ -681,6 +681,15 @@ static struct notifier_block gsmi_die_notifier = {
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static int gsmi_panic_callback(struct notifier_block *nb,
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unsigned long reason, void *arg)
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{
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/*
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* Panic callbacks are executed with all other CPUs stopped,
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* so we must not attempt to spin waiting for gsmi_dev.lock
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* to be released.
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*/
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if (spin_is_locked(&gsmi_dev.lock))
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return NOTIFY_DONE;
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gsmi_shutdown_reason(GSMI_SHUTDOWN_PANIC);
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return NOTIFY_DONE;
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}
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