[PATCH v2 03/13] firmware: google: Test spinlock on panic path to avoid lockups

Guilherme G. Piccoli
2022-07-19T19:55:29Z

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 <davidgow@google.com>
Cc: Evan Green <evgreen@chromium.org>
Cc: Julius Werner <jwerner@chromium.org>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>

---

V2:
- 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
review/idea!

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;
+
gsmi_shutdown_reason(GSMI_SHUTDOWN_PANIC);
return NOTIFY_DONE;
}
--
2.37.1