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firmware: google: test spinlock on panic path to avoid lockups

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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: 74c5b31c66 ("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>
This commit is contained in:
Guilherme G. Piccoli 2022-09-09 17:07:55 -03:00 committed by Andrew Morton
parent 5758478a3d
commit 1179083ff0
1 changed files with 9 additions and 0 deletions
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9
drivers/firmware/google/gsmi.c
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@ -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;
}