fs: optimize away ->_qproc indirection for poll_mask based polling

[Christoph Hellwig]

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 fs/select.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/fs/select.c b/fs/select.c
index bc3cc0f98896..54406e0ad23e 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -845,7 +845,25 @@ static inline __poll_t do_pollfd(struct pollfd *pollfd, poll_table *pwait,
 	/* userland u16 ->events contains POLL... bitmap */
 	filter = demangle_poll(pollfd->events) | EPOLLERR | EPOLLHUP;
 	pwait->_key = filter | busy_flag;
-	mask = vfs_poll(f.file, pwait);
+	if (f.file->f_op->poll) {
+		mask = f.file->f_op->poll(f.file, pwait);
+	} else if (file_has_poll_mask(f.file)) {
+		struct wait_queue_head *head;
+
+		head = f.file->f_op->get_poll_head(f.file, pwait->_key);
+		if (!head) {
+			mask = DEFAULT_POLLMASK;
+		} else if (IS_ERR(head)) {
+			mask = EPOLLERR;
+		} else {
+			if (pwait->_qproc)
+				__pollwait(f.file, head, pwait);
+			mask = f.file->f_op->poll_mask(f.file, pwait->_key);
+		}
+	} else {
+		mask = DEFAULT_POLLMASK;
+	}
+
 	if (mask & busy_flag)
 		*can_busy_poll = true;
 	mask &= filter;		/* Mask out unneeded events. */
-- 
2.17.1