BUG#24507 (rpl_log.test crash slave):

The problem was located to lie inside current NPTL pthread_exit() 
implementation. Race conditions in this code can lead to segmentation
fault. Hovewer, this can happen only in a race between first thread 
calling pthread_exit() and other threads. 

Workaround implemented in this patch spawns a dummy thread, which
exits immediately, during thread lib initialization. This will exclude
segment violations when further threads exit.

mysys/my_thr_init.c

@@ -44,6 +44,23 @@ pthread_mutexattr_t my_fast_mutexattr;
 pthread_mutexattr_t my_errorcheck_mutexattr;
 #endif
 
+#ifdef NPTL_PTHREAD_EXIT_BUG /* see my_pthread.h */
+
+/*
+ Dummy thread spawned in my_thread_global_init() below to avoid
+ race conditions in NPTL pthread_exit code.
+*/
+
+static
+pthread_handler_t nptl_pthread_exit_hack_handler(void *arg)
+{
+  /* Do nothing! */
+  pthread_exit(0);
+  return 0;
+}
+
+#endif
+
 /*
   initialize thread environment
 
@@ -62,6 +79,28 @@ my_bool my_thread_global_init(void)
     fprintf(stderr,"Can't initialize threads: error %d\n",errno);
     return 1;
   }
+  
+#ifdef NPTL_PTHREAD_EXIT_BUG
+
+/*
+  BUG#24507: Race conditions inside current NPTL pthread_exit() implementation.
+
+  To avoid a possible segmentation fault during concurrent executions of 
+  pthread_exit(), a dummy thread is spawned which initializes internal variables
+  of pthread lib. See bug description for thoroughfull explanation. 
+  
+  TODO: Remove this code when fixed versions of glibc6 are in common use. 
+*/
+
+  pthread_t       dummy_thread;
+  pthread_attr_t  dummy_thread_attr;
+
+  pthread_attr_init(&dummy_thread_attr);
+  pthread_attr_setdetachstate(&dummy_thread_attr,PTHREAD_CREATE_DETACHED);
+
+  pthread_create(&dummy_thread,&dummy_thread_attr,nptl_pthread_exit_hack_handler,NULL);
+
+#endif
 
 #ifdef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
   /*