firmware: Avoid deadlock of usermodehelper lock at shutdown

When a system goes to reboot/shutdown, it tries to disable the
usermode helper via usermodehelper_disable().  This might be blocked
when a driver tries to load a firmware beforehand and it's stuck by
some reason.  For example, dell_rbu driver loads the firmware in
non-hotplug mode and waits for user-space clearing the loading sysfs
flag.  If user-space doesn't clear the flag, it waits forever, thus
blocks the reboot, too.

As a workaround, in this patch, the firmware class driver registers a
reboot notifier so that it can abort all pending f/w bufs before
issuing usermodehelper_disable().

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Acked-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Conflicts:
	drivers/base/firmware_class.c

Change-Id: I7ff6c198cd34090e55845b9d4035b1e5dc86226b
diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index 01e2103..55d682e 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -27,6 +27,7 @@
 #include <linux/pm.h>
 #include <linux/suspend.h>
 #include <linux/syscore_ops.h>
+#include <linux/reboot.h>
 
 #include <generated/utsrelease.h>
 
@@ -130,6 +131,7 @@
 	struct page **pages;
 	int nr_pages;
 	int page_array_size;
+	struct list_head pending_list;
 #endif
 	char fw_id[];
 };
@@ -171,6 +173,9 @@
 	strcpy(buf->fw_id, fw_name);
 	buf->fwc = fwc;
 	init_completion(&buf->completion);
+#ifdef CONFIG_FW_LOADER_USER_HELPER
+	INIT_LIST_HEAD(&buf->pending_list);
+#endif
 
 	pr_debug("%s: fw-%s buf=%p\n", __func__, fw_name, buf);
 
@@ -446,10 +451,8 @@
 	return container_of(dev, struct firmware_priv, dev);
 }
 
-static void fw_load_abort(struct firmware_priv *fw_priv)
+static void __fw_load_abort(struct firmware_buf *buf)
 {
-	struct firmware_buf *buf = fw_priv->buf;
-
 	/*
 	 * There is a small window in which user can write to 'loading'
 	 * between loading done and disappearance of 'loading'
@@ -457,8 +460,16 @@
 	if (test_bit(FW_STATUS_DONE, &buf->status))
 		return;
 
+	list_del_init(&buf->pending_list);
 	set_bit(FW_STATUS_ABORT, &buf->status);
 	complete_all(&buf->completion);
+}
+
+static void fw_load_abort(struct firmware_priv *fw_priv)
+{
+	struct firmware_buf *buf = fw_priv->buf;
+
+	__fw_load_abort(buf);
 
 	/* avoid user action after loading abort */
 	fw_priv->buf = NULL;
@@ -467,6 +478,25 @@
 #define is_fw_load_aborted(buf)	\
 	test_bit(FW_STATUS_ABORT, &(buf)->status)
 
+static LIST_HEAD(pending_fw_head);
+
+/* reboot notifier for avoid deadlock with usermode_lock */
+static int fw_shutdown_notify(struct notifier_block *unused1,
+			      unsigned long unused2, void *unused3)
+{
+	mutex_lock(&fw_lock);
+	while (!list_empty(&pending_fw_head))
+		__fw_load_abort(list_first_entry(&pending_fw_head,
+					       struct firmware_buf,
+					       pending_list));
+	mutex_unlock(&fw_lock);
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block fw_shutdown_nb = {
+	.notifier_call = fw_shutdown_notify,
+};
+
 static ssize_t firmware_timeout_show(struct class *class,
 				     struct class_attribute *attr,
 				     char *buf)
@@ -619,6 +649,7 @@
 			 * is completed.
 			 * */
 			fw_map_pages_buf(fw_buf);
+			list_del_init(&fw_buf->pending_list);
 			complete_all(&fw_buf->completion);
 			break;
 		}
@@ -868,6 +899,10 @@
 		kobject_uevent(&fw_priv->dev.kobj, KOBJ_ADD);
 	}
 
+	mutex_lock(&fw_lock);
+	list_add(&buf->pending_list, &pending_fw_head);
+	mutex_unlock(&fw_lock);
+
 	wait_for_completion(&buf->completion);
 
 	cancel_delayed_work_sync(&fw_priv->timeout_work);
@@ -1526,6 +1561,7 @@
 {
 	fw_cache_init();
 #ifdef CONFIG_FW_LOADER_USER_HELPER
+	register_reboot_notifier(&fw_shutdown_nb);
 	return class_register(&firmware_class);
 #else
 	return 0;
@@ -1539,6 +1575,7 @@
 	unregister_pm_notifier(&fw_cache.pm_notify);
 #endif
 #ifdef CONFIG_FW_LOADER_USER_HELPER
+	unregister_reboot_notifier(&fw_shutdown_nb);
 	class_unregister(&firmware_class);
 #endif
 }