epoll: simplify signal handling

Check signals before locking ep->lock, and immediately return -EINTR if
there is any signal pending.

This saves a few loads, stores, and branches from the hot path and
simplifies the loop structure for follow up patches.

Link: https://lkml.kernel.org/r/20201106231635.3528496-3-soheil.kdev@gmail.com
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 935c66c..4f460be 100644 (file)
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1733,7 +1733,7 @@ static inline struct timespec64 ep_set_mstimeout(long ms)
 static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
                   int maxevents, long timeout)
 {
-       int res = 0, eavail, timed_out = 0;
+       int res, eavail, timed_out = 0;
        u64 slack = 0;
        wait_queue_entry_t wait;
        ktime_t expires, *to = NULL;
@@ -1780,6 +1780,9 @@ fetch_events:
        ep_reset_busy_poll_napi_id(ep);
 
        do {
+               if (signal_pending(current))
+                       return -EINTR;
+
                /*
                 * Internally init_wait() uses autoremove_wake_function(),
                 * thus wait entry is removed from the wait queue on each
@@ -1809,15 +1812,12 @@ fetch_events:
                 * important.
                 */
                eavail = ep_events_available(ep);
-               if (!eavail) {
-                       if (signal_pending(current))
-                               res = -EINTR;
-                       else
-                               __add_wait_queue_exclusive(&ep->wq, &wait);
-               }
+               if (!eavail)
+                       __add_wait_queue_exclusive(&ep->wq, &wait);
+
                write_unlock_irq(&ep->lock);
 
-               if (!eavail && !res)
+               if (!eavail)
                        timed_out = !schedule_hrtimeout_range(to, slack,
                                                              HRTIMER_MODE_ABS);
 
@@ -1853,14 +1853,14 @@ send_events:
                 * finding more events available and fetching
                 * repeatedly.
                 */
-               res = -EINTR;
+               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
         * more luck.
         */
-       if (!res && eavail &&
+       if (eavail &&
            !(res = ep_send_events(ep, events, maxevents)) && !timed_out)
                goto fetch_events;