commit a58ad3f801960fa0dc0bb1106eb0d99f7ebd77b1
Author: Roland McGrath <roland@hack.frob.com>
Date:   Thu Jun 13 15:09:29 2013 -0700

    Fix raciness in waitid test.

diff --git a/posix/tst-waitid.c b/posix/tst-waitid.c
index f8a302ea3153a853..d63ad65fbefc64ad 100644
--- a/posix/tst-waitid.c
+++ b/posix/tst-waitid.c
@@ -145,7 +145,7 @@ do_test (int argc, char *argv[])
   /* Give the child a chance to stop.  */
   sleep (3);
 
-  CHECK_SIGCHLD ("stopped", CLD_STOPPED, SIGSTOP);
+  CHECK_SIGCHLD ("stopped (before waitid)", CLD_STOPPED, SIGSTOP);
 
   /* Now try a wait that should not succeed.  */
   siginfo_t info;
@@ -227,7 +227,7 @@ do_test (int argc, char *argv[])
       expecting_sigchld = 0;
     }
   else
-    CHECK_SIGCHLD ("continued", CLD_CONTINUED, SIGCONT);
+    CHECK_SIGCHLD ("continued (before waitid)", CLD_CONTINUED, SIGCONT);
 
   info.si_signo = 0;		/* A successful call sets it to SIGCHLD.  */
   info.si_pid = -1;
@@ -336,6 +336,13 @@ do_test (int argc, char *argv[])
       printf ("kill (%d, SIGSTOP): %m\n", pid);
       RETURN (EXIT_FAILURE);
     }
+
+  /* Give the child a chance to stop.  The waitpid call below will block
+     until it has stopped, but if we are real quick and enter the waitpid
+     system call before the SIGCHLD has been generated, then it will be
+     discarded and never delivered.  */
+  sleep (3);
+
   pid_t wpid = waitpid (pid, &fail, WUNTRACED);
   if (wpid < 0)
     {
@@ -354,7 +361,7 @@ do_test (int argc, char *argv[])
       printf ("waitpid WUNTRACED on stopped: status %x\n", fail);
       RETURN (EXIT_FAILURE);
     }
-  CHECK_SIGCHLD ("stopped", CLD_STOPPED, SIGSTOP);
+  CHECK_SIGCHLD ("stopped (after waitpid)", CLD_STOPPED, SIGSTOP);
 
   expecting_sigchld = 1;
   if (kill (pid, SIGCONT) != 0)
@@ -372,7 +379,7 @@ do_test (int argc, char *argv[])
       expecting_sigchld = 0;
     }
   else
-    CHECK_SIGCHLD ("continued", CLD_CONTINUED, SIGCONT);
+    CHECK_SIGCHLD ("continued (before waitpid)", CLD_CONTINUED, SIGCONT);
 
   wpid = waitpid (pid, &fail, WCONTINUED);
   if (wpid < 0)