zos: lock protect global epoll list in epoll_ctl

This will eliminate a race condition that occurs between
epoll_close_fd, epoll_ctl and epoll_create in the
signal_multiple_loops test.

PR-URL: https://github.com/libuv/libuv/pull/1560
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

src/unix/os390-syscalls.c

@@ -130,17 +130,17 @@ static void epoll_init(void) {
 uv__os390_epoll* epoll_create1(int flags) {
   uv__os390_epoll* lst;
 
-  uv_once(&once, epoll_init);
-  uv_mutex_lock(&global_epoll_lock);
   lst = uv__malloc(sizeof(*lst));
-  if (lst == -1)
-    return NULL;
-  QUEUE_INSERT_TAIL(&global_epoll_queue, &lst->member);
-  uv_mutex_unlock(&global_epoll_lock);
+  if (lst != NULL) {
+    /* initialize list */
+    lst->size = 0;
+    lst->items = NULL;
+    uv_once(&once, epoll_init);
+    uv_mutex_lock(&global_epoll_lock);
+    QUEUE_INSERT_TAIL(&global_epoll_queue, &lst->member);
+    uv_mutex_unlock(&global_epoll_lock);
+  }
 
-  /* initialize list */
-  lst->size = 0;
-  lst->items = NULL;
   return lst;
 }
 
@@ -149,8 +149,11 @@ int epoll_ctl(uv__os390_epoll* lst,
               int op,
               int fd,
               struct epoll_event *event) {
+  uv_mutex_lock(&global_epoll_lock);
+
   if(op == EPOLL_CTL_DEL) {
     if (fd >= lst->size || lst->items[fd].fd == -1) {
+      uv_mutex_unlock(&global_epoll_lock);
       errno = ENOENT;
       return -1;
     }
@@ -158,6 +161,7 @@ int epoll_ctl(uv__os390_epoll* lst,
   } else if(op == EPOLL_CTL_ADD) {
     maybe_resize(lst, fd + 1);
     if (lst->items[fd].fd != -1) {
+      uv_mutex_unlock(&global_epoll_lock);
       errno = EEXIST;
       return -1;
     }
@@ -165,6 +169,7 @@ int epoll_ctl(uv__os390_epoll* lst,
     lst->items[fd].events = event->events;
   } else if(op == EPOLL_CTL_MOD) {
     if (fd >= lst->size || lst->items[fd].fd == -1) {
+      uv_mutex_unlock(&global_epoll_lock);
       errno = ENOENT;
       return -1;
     }
@@ -172,6 +177,7 @@ int epoll_ctl(uv__os390_epoll* lst,
   } else
     abort();
 
+  uv_mutex_unlock(&global_epoll_lock);
   return 0;
 }
 

src/unix/os390.c

@@ -117,7 +117,7 @@ void uv_loadavg(double avg[3]) {
 int uv__platform_loop_init(uv_loop_t* loop) {
   uv__os390_epoll* ep;
 
-  ep = epoll_create1(UV__EPOLL_CLOEXEC);
+  ep = epoll_create1(0);
   loop->ep = ep;
   if (ep == NULL)
     return -errno;