io.c (fptr_finalize_flush): close race leading to EBADF

The previous ordering was:

a) notify waiting_fd threads of impending close
b) waiting on busy list from a)
c) invalidate fptr->fd
d) calling close()

However, it was possible for a new thread to enter
the waiting_fd list while scheduling on b), leading
to EBADF from those threads when we hit d).

Instead, we now avoid triggering EBADF in other threads by
reordering b) and c)

a) notify waiting_fd threads of impending close
c) invalidate fptr->fd
b) waiting on busy list from a)
d) calling close()

cf. http://ci.rvm.jp/results/trunk-nopara@silicon-docker/1474526

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65937 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

io.c

@@ -4552,7 +4552,8 @@ static void free_io_buffer(rb_io_buffer_t *buf);
 static void clear_codeconv(rb_io_t *fptr);
 
 static void
-fptr_finalize_flush(rb_io_t *fptr, int noraise, int keepgvl)
+fptr_finalize_flush(rb_io_t *fptr, int noraise, int keepgvl,
+                    struct list_head *busy)
 {
     VALUE err = Qnil;
     int fd = fptr->fd;
@@ -4584,6 +4585,14 @@ fptr_finalize_flush(rb_io_t *fptr, int noraise, int keepgvl)
     fptr->stdio_file = 0;
     fptr->mode &= ~(FMODE_READABLE|FMODE_WRITABLE);
 
+    /*
+     * ensure waiting_fd users do not hit EBADF, wait for them
+     * to exit before we call close().
+     */
+    if (busy) {
+        do rb_thread_schedule(); while (!list_empty(busy));
+    }
+
     if (IS_PREP_STDIO(fptr) || fd <= 2) {
 	/* need to keep FILE objects of stdin, stdout and stderr */
     }
@@ -4616,7 +4625,7 @@ fptr_finalize_flush(rb_io_t *fptr, int noraise, int keepgvl)
 static void
 fptr_finalize(rb_io_t *fptr, int noraise)
 {
-    fptr_finalize_flush(fptr, noraise, FALSE);
+    fptr_finalize_flush(fptr, noraise, FALSE, 0);
     free_io_buffer(&fptr->rbuf);
     free_io_buffer(&fptr->wbuf);
     clear_codeconv(fptr);
@@ -4741,8 +4750,8 @@ io_close_fptr(VALUE io)
     if (fptr->fd < 0) return 0;
 
     if (rb_notify_fd_close(fptr->fd, &busy)) {
-	fptr_finalize_flush(fptr, FALSE, KEEPGVL); /* calls close(fptr->fd) */
-	do rb_thread_schedule(); while (!list_empty(&busy));
+        /* calls close(fptr->fd): */
+        fptr_finalize_flush(fptr, FALSE, KEEPGVL, &busy);
     }
     rb_io_fptr_cleanup(fptr, FALSE);
     return fptr;