nptl: Fix race between pthread_kill and thread exit (bug 12889)

A new thread exit lock and flag are introduced.  They are used to
detect that the thread is about to exit or has exited in
__pthread_kill_internal, and the signal is not sent in this case.

The test sysdeps/pthread/tst-pthread_cancel-select-loop.c is derived
from a downstream test originally written by Marek Polacek.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
index 7607f36..a559f86 100644
--- a/nptl/pthread_create.c
+++ b/nptl/pthread_create.c
@@ -36,6 +36,7 @@
 #include <sys/single_threaded.h>
 #include <version.h>
 #include <clone_internal.h>
+#include <futex-internal.h>
 
 #include <shlib-compat.h>
 
@@ -484,6 +485,19 @@ start_thread (void *arg)
     /* This was the last thread.  */
     exit (0);
 
+  /* This prevents sending a signal from this thread to itself during
+     its final stages.  This must come after the exit call above
+     because atexit handlers must not run with signals blocked.  */
+  __libc_signal_block_all (NULL);
+
+  /* Tell __pthread_kill_internal that this thread is about to exit.
+     If there is a __pthread_kill_internal in progress, this delays
+     the thread exit until the signal has been queued by the kernel
+     (so that the TID used to send it remains valid).  */
+  __libc_lock_lock (pd->exit_lock);
+  pd->exiting = true;
+  __libc_lock_unlock (pd->exit_lock);
+
 #ifndef __ASSUME_SET_ROBUST_LIST
   /* If this thread has any robust mutexes locked, handle them now.  */
 # if __PTHREAD_MUTEX_HAVE_PREV