+ firmware-google-test-spinlock-on-panic-path-to-avoid-lockups.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

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@igalia.com>
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@igalia.com
Fixes: 74c5b31c6618 ("driver: Google EFI SMI")
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Reviewed-by: Evan Green <evgreen@chromium.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: David Gow <davidgow@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Julius Werner <jwerner@chromium.org>
Cc: Petr Mladek <pmladek@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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@igalia.com are

firmware-google-test-spinlock-on-panic-path-to-avoid-lockups.patch