On Tue, Jul 19, 2022 at 12:55 PM Guilherme G. Piccoli
[off-list ref] 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 <redacted>
Cc: Evan Green <redacted>
Cc: Julius Werner <jwerner@chromium.org>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>

Reviewed-by: Evan Green <redacted>