epoll: pull fatal signal checks into ep_send_events()

To simplify the code, pull in checking the fatal signals into
ep_send_events().  ep_send_events() is called only from ep_poll().

Note that, previously, we were always checking fatal events, but it is
checked only if eavail is true.  This should be fine because the goal of
that check is to quickly return from epoll_wait() when there is a pending
fatal signal.

Link: https://lkml.kernel.org/r/20201106231635.3528496-4-soheil.kdev@gmail.com
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Suggested-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Khazhismel Kumykov <khazhy@google.com>
Cc: Guantao Liu <guantaol@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: soheilhy

fs/eventpoll.c

@@ -1625,6 +1625,14 @@ static int ep_send_events(struct eventpoll *ep,
 	poll_table pt;
 	int res = 0;
 
+	/*
+	 * Always short-circuit for fatal signals to allow threads to make a
+	 * timely exit without the chance of finding more events available and
+	 * fetching repeatedly.
+	 */
+	if (fatal_signal_pending(current))
+		return -EINTR;
+
 	init_poll_funcptr(&pt, NULL);
 
 	mutex_lock(&ep->mtx);
@@ -1846,15 +1854,6 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
 	}
 
 send_events:
-	if (fatal_signal_pending(current)) {
-		/*
-		 * Always short-circuit for fatal signals to allow
-		 * threads to make a timely exit without the chance of
-		 * finding more events available and fetching
-		 * repeatedly.
-		 */
-		return -EINTR;
-	}
 	/*
 	 * Try to transfer events to user space. In case we get 0 events and
 	 * there's still timeout left over, we go trying again in search of