ANDROID: goldfish: goldfish_pipe: fix locking errors

NOTE: This is a cherry-pick of the kernel/common/android-4.4 patch
      37e461fc into the kernel/goldfish/android-goldfish-3.10 branch.

If the get_user_pages_fast() call in goldfish_pipe_read_write() failed,
it would return while still holding pipe->lock.

goldfish_pipe_read_write() later releases and tries to re-acquire
pipe->lock.  If the re-acquire call failed, goldfish_pipe_read_write()
would try unlock pipe->lock on exit anyway.

This fixes the smatch messages:

drivers/platform/goldfish/goldfish_pipe.c:392 goldfish_pipe_read_write() error: double unlock 'mutex:&pipe->lock'
drivers/platform/goldfish/goldfish_pipe.c:397 goldfish_pipe_read_write() warn: inconsistent returns 'mutex:&pipe->lock'.

Change-Id: Id60afd6c191f69af86386405d397b6ad2dd37079
Signed-off-by: Greg Hackmann <ghackmann@google.com>

drivers/platform/goldfish/goldfish_pipe.c

@@ -279,11 +279,13 @@ static ssize_t goldfish_pipe_read_write(struct file *filp, char __user *buffer,
 		if (ret == 0) {
 			DPRINT("%s: error: (requested pages == 0) (wanted %d)\n",
 					__FUNCTION__, requested_pages);
+			mutex_unlock(&pipe->lock);
 			return ret;
 		}
 		if (ret < 0) {
 			DPRINT("%s: (requested pages < 0) %d \n",
 				 	__FUNCTION__, requested_pages);
+			mutex_unlock(&pipe->lock);
 			return ret;
 		}
 
@@ -395,10 +397,8 @@ static ssize_t goldfish_pipe_read_write(struct file *filp, char __user *buffer,
 		}
 
 		/* Try to re-acquire the lock */
-		if (mutex_lock_interruptible(&pipe->lock)) {
-			ret = -ERESTARTSYS;
-			break;
-		}
+		if (mutex_lock_interruptible(&pipe->lock))
+			return -ERESTARTSYS;
 	}
 	mutex_unlock(&pipe->lock);