HID: hidraw: fix nonblock read return EAGAIN after device removed

When nonblock read the condition check (file->f_flags & O_NONBLOCK) always be
true, signal_pending and device exist checking never get a chance to run, so
the user mode code always get EAGAIN even if device removed. move nonblock mode
checking to the last can fix this problem.
Signed-off-by: NFounder Fang <founder.fang@gmail.com>
Reviewed-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

drivers/hid/hidraw.c

@@ -57,10 +57,6 @@ static ssize_t hidraw_read(struct file *file, char __user *buffer, size_t count,
 			set_current_state(TASK_INTERRUPTIBLE);
 
 			while (list->head == list->tail) {
-				if (file->f_flags & O_NONBLOCK) {
-					ret = -EAGAIN;
-					break;
-				}
 				if (signal_pending(current)) {
 					ret = -ERESTARTSYS;
 					break;
@@ -69,6 +65,10 @@ static ssize_t hidraw_read(struct file *file, char __user *buffer, size_t count,
 					ret = -EIO;
 					break;
 				}
+				if (file->f_flags & O_NONBLOCK) {
+					ret = -EAGAIN;
+					break;
+				}
 
 				/* allow O_NONBLOCK to work well from other threads */
 				mutex_unlock(&list->read_mutex);