[PATCH 4.9 109/159] firmware: google: Test spinlock on panic path to avoid lockups

[Greg Kroah-Hartman]

From: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx>

[ 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@xxxxxxxxxxxxxxxxxxxx>
Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
Cc: David Gow <davidgow@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Julius Werner <jwerner@xxxxxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Reviewed-by: Evan Green <evgreen@xxxxxxxxxxxx>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20220909200755.189679-1-gpiccoli@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 98cdfc2ee0df..6fd5f6776735 100644
--- a/drivers/firmware/google/gsmi.c
+++ b/drivers/firmware/google/gsmi.c
@@ -661,6 +661,15 @@ 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