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Date:   Tue, 19 Jul 2022 16:53:16 -0300
From:   "Guilherme G. Piccoli" <>
Cc:,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, "Guilherme G. Piccoli" <>,, Ard Biesheuvel <>,
        David Gow <>,
        Evan Green <>,
        Julius Werner <>
Subject: [PATCH v2 03/13] 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.

Fixes: 74c5b31c6618 ("driver: Google EFI SMI")
Cc: Ard Biesheuvel <>
Cc: David Gow <>
Cc: Evan Green <>
Cc: Julius Werner <>
Signed-off-by: Guilherme G. Piccoli <>


- do not use spin_trylock anymore, to avoid messing with
non-panic paths; now we just check the spinlock state in
the panic notifier before taking it. Thanks Evan for the

 drivers/firmware/google/gsmi.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/firmware/google/gsmi.c b/drivers/firmware/google/gsmi.c
index adaa492c3d2d..3ef5f3c0b4e4 100644
--- a/drivers/firmware/google/gsmi.c
+++ b/drivers/firmware/google/gsmi.c
@@ -681,6 +681,14 @@ static struct notifier_block gsmi_die_notifier = {
 static int gsmi_panic_callback(struct notifier_block *nb,
 			       unsigned long reason, void *arg)
+	/*
+	 * Perform the lock check before effectively trying
+	 * to acquire it on gsmi_shutdown_reason() to avoid
+	 * potential lockups in atomic context.
+	 */
+	if (spin_is_locked(&gsmi_dev.lock))
+		return NOTIFY_DONE;
 	return NOTIFY_DONE;

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