[PATCH 04/30] firmware: google: Convert regular spinlock into trylock on panic path

Guilherme G. Piccoli
2022-04-27T22:48:58Z

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, local IRQs and all other CPUs that aren't running the
current panic function.

With that said, taking a spinlock in this scenario is a
dangerous invitation for a deadlock scenario. So, we fix
that in this commit by changing the regular spinlock with
a trylock, which is a safer approach.

Fixes: 74c5b31c6618 ("driver: Google EFI SMI")
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: David Gow <davidgow@google.com>
Cc: Evan Green <evgreen@chromium.org>
Cc: Julius Werner <jwerner@chromium.org>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
---
drivers/firmware/google/gsmi.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/google/gsmi.c b/drivers/firmware/google/gsmi.c
index adaa492c3d2d..b01ed02e4a87 100644
--- a/drivers/firmware/google/gsmi.c
+++ b/drivers/firmware/google/gsmi.c
@@ -629,7 +629,10 @@ static int gsmi_shutdown_reason(int reason)
if (saved_reason & (1 << reason))
return 0;

- spin_lock_irqsave(&gsmi_dev.lock, flags);
+ if (!spin_trylock_irqsave(&gsmi_dev.lock, flags)) {
+ rc = -EBUSY;
+ goto out;
+ }

saved_reason |= (1 << reason);

@@ -646,6 +649,7 @@ static int gsmi_shutdown_reason(int reason)

spin_unlock_irqrestore(&gsmi_dev.lock, flags);

+out:
if (rc < 0)
printk(KERN_ERR "gsmi: Log Shutdown Reason failed\n");
else
--
2.36.0