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

3 files changed, 18 insertions, 22 deletions

diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index 6c9387d646ec..deee871e509c 100644
--- a/drivers/base/firmware_class.c
+++ b/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;
diff --git a/include/linux/kmod.h b/include/linux/kmod.h
index 9efeae679106..97d22c3e08b1 100644
--- a/include/linux/kmod.h
+++ b/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__ */
diff --git a/kernel/kmod.c b/kernel/kmod.c
index 957a7aab8ebc..4079ac1d5e79 100644
--- a/kernel/kmod.c
+++ b/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);