splice: fix infinite loop in generic_file_splice_read()

There's a quirky loop in generic_file_splice_read() that could go
on indefinitely, if the file splice returns 0 permanently (and not
just as a temporary condition). Get rid of the loop and pass
back -EAGAIN correctly from __generic_file_splice_read(), so we
handle that condition properly as well.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

fs/splice.c

@@ -370,8 +370,10 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
 			 * for an in-flight io page
 			 */
 			if (flags & SPLICE_F_NONBLOCK) {
-				if (TestSetPageLocked(page))
+				if (TestSetPageLocked(page)) {
+					error = -EAGAIN;
 					break;
+				}
 			} else
 				lock_page(page);
 
@@ -479,9 +481,8 @@ ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
 				 struct pipe_inode_info *pipe, size_t len,
 				 unsigned int flags)
 {
-	ssize_t spliced;
-	int ret;
 	loff_t isize, left;
+	int ret;
 
 	isize = i_size_read(in->f_mapping->host);
 	if (unlikely(*ppos >= isize))
@@ -491,29 +492,9 @@ ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
 	if (unlikely(left < len))
 		len = left;
 
-	ret = 0;
-	spliced = 0;
-	while (len && !spliced) {
-		ret = __generic_file_splice_read(in, ppos, pipe, len, flags);
-
-		if (ret < 0)
-			break;
-		else if (!ret) {
-			if (spliced)
-				break;
-			if (flags & SPLICE_F_NONBLOCK) {
-				ret = -EAGAIN;
-				break;
-			}
-		}
-
+	ret = __generic_file_splice_read(in, ppos, pipe, len, flags);
+	if (ret > 0)
 		*ppos += ret;
-		len -= ret;
-		spliced += ret;
-	}
-
-	if (spliced)
-		return spliced;
 
 	return ret;
 }