linux: remove epoll_pwait() emulation code path (libuv#3936)

This was removed before in 2018 but then reinstated again in 2019 to
fix building with old Android SDKs. Well, time marches on; this time
it's gone for good.

Refs: libuv#1372
Refs: libuv#2358

src/unix/linux.c

@@ -307,18 +307,14 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
    * that being the largest value I have seen in the wild (and only once.)
    */
   static const int max_safe_timeout = 1789569;
-  static int no_epoll_pwait_cached;
-  static int no_epoll_wait_cached;
-  int no_epoll_pwait;
-  int no_epoll_wait;
   struct epoll_event events[1024];
   struct epoll_event* pe;
   struct epoll_event e;
   int real_timeout;
   QUEUE* q;
   uv__io_t* w;
+  sigset_t* sigmask;
   sigset_t sigset;
-  uint64_t sigmask;
   uint64_t base;
   int have_signals;
   int nevents;
@@ -372,11 +368,11 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
     w->events = w->pevents;
   }
 
-  sigmask = 0;
+  sigmask = NULL;
   if (loop->flags & UV_LOOP_BLOCK_SIGPROF) {
     sigemptyset(&sigset);
     sigaddset(&sigset, SIGPROF);
-    sigmask |= 1 << (SIGPROF - 1);
+    sigmask = &sigset;
   }
 
   assert(timeout >= -1);
@@ -393,15 +389,6 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
     user_timeout = 0;
   }
 
-  /* You could argue there is a dependency between these two but
-   * ultimately we don't care about their ordering with respect
-   * to one another. Worst case, we make a few system calls that
-   * could have been avoided because another thread already knows
-   * they fail with ENOSYS. Hardly the end of the world.
-   */
-  no_epoll_pwait = uv__load_relaxed(&no_epoll_pwait_cached);
-  no_epoll_wait = uv__load_relaxed(&no_epoll_wait_cached);
-
   for (;;) {
     /* Only need to set the provider_entry_time if timeout != 0. The function
      * will return early if the loop isn't configured with UV_METRICS_IDLE_TIME.
@@ -415,34 +402,11 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
     if (sizeof(int32_t) == sizeof(long) && timeout >= max_safe_timeout)
       timeout = max_safe_timeout;
 
-    if (sigmask != 0 && no_epoll_pwait != 0)
-      if (pthread_sigmask(SIG_BLOCK, &sigset, NULL))
-        abort();
-
-    if (no_epoll_wait != 0 || (sigmask != 0 && no_epoll_pwait == 0)) {
-      nfds = epoll_pwait(loop->backend_fd,
-                         events,
-                         ARRAY_SIZE(events),
-                         timeout,
-                         &sigset);
-      if (nfds == -1 && errno == ENOSYS) {
-        uv__store_relaxed(&no_epoll_pwait_cached, 1);
-        no_epoll_pwait = 1;
-      }
-    } else {
-      nfds = epoll_wait(loop->backend_fd,
-                        events,
-                        ARRAY_SIZE(events),
-                        timeout);
-      if (nfds == -1 && errno == ENOSYS) {
-        uv__store_relaxed(&no_epoll_wait_cached, 1);
-        no_epoll_wait = 1;
-      }
-    }
-
-    if (sigmask != 0 && no_epoll_pwait != 0)
-      if (pthread_sigmask(SIG_UNBLOCK, &sigset, NULL))
-        abort();
+    nfds = epoll_pwait(loop->backend_fd,
+                       events,
+                       ARRAY_SIZE(events),
+                       timeout,
+                       sigmask);
 
     /* Update loop->time unconditionally. It's tempting to skip the update when
      * timeout == 0 (i.e. non-blocking poll) but there is no guarantee that the
@@ -471,12 +435,6 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
     }
 
     if (nfds == -1) {
-      if (errno == ENOSYS) {
-        /* epoll_wait() or epoll_pwait() failed, try the other system call. */
-        assert(no_epoll_wait == 0 || no_epoll_pwait == 0);
-        continue;
-      }
-
       if (errno != EINTR)
         abort();