eventfd: only return events requested in poll_mask()

The ->poll_mask() operation has a mask of events that the caller
is interested in, but we're returning all events regardless.

Change to return only the events the caller is interested in. This
fixes aio IO_CMD_POLL returning immediately when called with POLLIN
on an eventfd, since an eventfd is almost always ready for a write.
Signed-off-by: Avi Kivity <avi@scylladb.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/eventfd.c

@@ -156,11 +156,11 @@ static __poll_t eventfd_poll_mask(struct file *file, __poll_t eventmask)
 	count = READ_ONCE(ctx->count);
 
 	if (count > 0)
-		events |= EPOLLIN;
+		events |= (EPOLLIN & eventmask);
 	if (count == ULLONG_MAX)
 		events |= EPOLLERR;
 	if (ULLONG_MAX - 1 > count)
-		events |= EPOLLOUT;
+		events |= (EPOLLOUT & eventmask);
 
 	return events;
 }