fs: cleanup do_pollfd

Use straightline code with failure handling gotos instead of a lot
of nested conditionals.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/select.c

@@ -812,34 +812,32 @@ static inline __poll_t do_pollfd(struct pollfd *pollfd, poll_table *pwait,
 				     bool *can_busy_poll,
 				     __poll_t busy_flag)
 {
-	__poll_t mask;
-	int fd;
-
-	mask = 0;
-	fd = pollfd->fd;
-	if (fd >= 0) {
-		struct fd f = fdget(fd);
-		mask = EPOLLNVAL;
-		if (f.file) {
-			/* userland u16 ->events contains POLL... bitmap */
-			__poll_t filter = demangle_poll(pollfd->events) |
-						EPOLLERR | EPOLLHUP;
-			mask = DEFAULT_POLLMASK;
-			if (f.file->f_op->poll) {
-				pwait->_key = filter;
-				pwait->_key |= busy_flag;
-				mask = f.file->f_op->poll(f.file, pwait);
-				if (mask & busy_flag)
-					*can_busy_poll = true;
-			}
-			/* Mask out unneeded events. */
-			mask &= filter;
-			fdput(f);
-		}
+	int fd = pollfd->fd;
+	__poll_t mask = 0, filter;
+	struct fd f;
+
+	if (fd < 0)
+		goto out;
+	mask = EPOLLNVAL;
+	f = fdget(fd);
+	if (!f.file)
+		goto out;
+
+	/* userland u16 ->events contains POLL... bitmap */
+	filter = demangle_poll(pollfd->events) | EPOLLERR | EPOLLHUP;
+	mask = DEFAULT_POLLMASK;
+	if (f.file->f_op->poll) {
+		pwait->_key = filter | busy_flag;
+		mask = f.file->f_op->poll(f.file, pwait);
+		if (mask & busy_flag)
+			*can_busy_poll = true;
 	}
+	mask &= filter;		/* Mask out unneeded events. */
+	fdput(f);
+
+out:
 	/* ... and so does ->revents */
 	pollfd->revents = mangle_poll(mask);
-
 	return mask;
 }