PM: Print a warning if firmware is requested when tasks are frozen

Some drivers erroneously use request_firmware() from their ->resume()
(or ->thaw(), or ->restore()) callbacks, which is not going to work
unless the firmware has been built in.  This causes system resume to
stall until the firmware-loading timeout expires, which makes users
think that the resume has failed and reboot their machines
unnecessarily.  For this reason, make _request_firmware() print a
warning and return immediately with error code if it has been called
when tasks are frozen and it's impossible to start any new usermode
helpers.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Reviewed-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>

drivers/base/firmware_class.c

@@ -521,6 +521,11 @@ static int _request_firmware(const struct firmware **firmware_p,
 	if (!firmware_p)
 		return -EINVAL;
 
+	if (WARN_ON(usermodehelper_is_disabled())) {
+		dev_err(device, "firmware: %s will not be loaded\n", name);
+		return -EBUSY;
+	}
+
 	*firmware_p = firmware = kzalloc(sizeof(*firmware), GFP_KERNEL);
 	if (!firmware) {
 		dev_err(device, "%s: kmalloc(struct firmware) failed\n",

include/linux/kmod.h

@@ -111,7 +111,12 @@ call_usermodehelper(char *path, char **argv, char **envp, enum umh_wait wait)
 
 extern void usermodehelper_init(void);
 
+#ifdef CONFIG_PM_SLEEP
 extern int usermodehelper_disable(void);
 extern void usermodehelper_enable(void);
+extern bool usermodehelper_is_disabled(void);
+#else
+static inline bool usermodehelper_is_disabled(void) { return false; }
+#endif
 
 #endif /* __LINUX_KMOD_H__ */

kernel/kmod.c

@@ -301,6 +301,15 @@ void usermodehelper_enable(void)
 	usermodehelper_disabled = 0;
 }
 
+/**
+ * usermodehelper_is_disabled - check if new helpers are allowed to be started
+ */
+bool usermodehelper_is_disabled(void)
+{
+	return usermodehelper_disabled;
+}
+EXPORT_SYMBOL_GPL(usermodehelper_is_disabled);
+
 static void helper_lock(void)
 {
 	atomic_inc(&running_helpers);