firmware_class: Rework usermodehelper check

Instead of two functions, read_lock_usermodehelper() and
usermodehelper_is_disabled(), used in combination, introduce
usermodehelper_read_trylock() that will only return with umhelper_sem
held if usermodehelper_disabled is unset (and will return -EAGAIN
otherwise) and make _request_firmware() use it.

Rename read_unlock_usermodehelper() to
usermodehelper_read_unlock() to follow the naming convention of the
new function.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: stable@vger.kernel.org

drivers/base/firmware_class.c

@@ -533,12 +533,10 @@ static int _request_firmware(const struct firmware **firmware_p,
 		return 0;
 	}
 
-	read_lock_usermodehelper();
-
-	if (WARN_ON(usermodehelper_is_disabled())) {
+	retval = usermodehelper_read_trylock();
+	if (WARN_ON(retval)) {
 		dev_err(device, "firmware: %s will not be loaded\n", name);
-		retval = -EBUSY;
-		goto out;
+		goto out_nolock;
 	}
 
 	if (uevent)
@@ -573,8 +571,9 @@ static int _request_firmware(const struct firmware **firmware_p,
 	fw_destroy_instance(fw_priv);
 
 out:
-	read_unlock_usermodehelper();
+	usermodehelper_read_unlock();
 
+out_nolock:
 	if (retval) {
 		release_firmware(firmware);
 		*firmware_p = NULL;

include/linux/kmod.h

@@ -114,8 +114,7 @@ extern void usermodehelper_init(void);
 
 extern int usermodehelper_disable(void);
 extern void usermodehelper_enable(void);
-extern bool usermodehelper_is_disabled(void);
-extern void read_lock_usermodehelper(void);
-extern void read_unlock_usermodehelper(void);
+extern int usermodehelper_read_trylock(void);
+extern void usermodehelper_read_unlock(void);
 
 #endif /* __LINUX_KMOD_H__ */

kernel/kmod.c

@@ -339,17 +339,24 @@ static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
  */
 #define RUNNING_HELPERS_TIMEOUT	(5 * HZ)
 
-void read_lock_usermodehelper(void)
+int usermodehelper_read_trylock(void)
 {
+	int ret = 0;
+
 	down_read(&umhelper_sem);
+	if (usermodehelper_disabled) {
+		up_read(&umhelper_sem);
+		ret = -EAGAIN;
+	}
+	return ret;
 }
-EXPORT_SYMBOL_GPL(read_lock_usermodehelper);
+EXPORT_SYMBOL_GPL(usermodehelper_read_trylock);
 
-void read_unlock_usermodehelper(void)
+void usermodehelper_read_unlock(void)
 {
 	up_read(&umhelper_sem);
 }
-EXPORT_SYMBOL_GPL(read_unlock_usermodehelper);
+EXPORT_SYMBOL_GPL(usermodehelper_read_unlock);
 
 /**
  * usermodehelper_disable - prevent new helpers from being started
@@ -390,15 +397,6 @@ void usermodehelper_enable(void)
 	up_write(&umhelper_sem);
 }
 
-/**
- * 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);