The patch titled
Subject: firmware: google: test spinlock on panic path to avoid lockups
has been added to the -mm mm-nonmm-unstable branch. Its filename is
firmware-google-test-spinlock-on-panic-path-to-avoid-lockups.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/firmware-google-test-spinlock-on-panic-path-to-avoid-lockups.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: "Guilherme G. Piccoli" <gpiccoli@xxxxxxxxxx>
Subject: firmware: google: test spinlock on panic path to avoid lockups
Date: Fri, 9 Sep 2022 17:07:55 -0300
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@xxxxxxxxxx
Fixes: 74c5b31c6618 ("driver: Google EFI SMI")
Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx>
Reviewed-by: Evan Green <evgreen@xxxxxxxxxxxx>
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>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/firmware/google/gsmi.c | 9 +++++++++
1 file changed, 9 insertions(+)
--- a/drivers/firmware/google/gsmi.c~firmware-google-test-spinlock-on-panic-path-to-avoid-lockups
+++ a/drivers/firmware/google/gsmi.c
@@ -681,6 +681,15 @@ static struct notifier_block gsmi_die_no
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;
}
_
Patches currently in -mm which might be from gpiccoli@xxxxxxxxxx are
firmware-google-test-spinlock-on-panic-path-to-avoid-lockups.patch
