malloc: Fix attached thread reference count handling [BZ #19243]

reused_arena can increase the attached thread count of arenas on the
free list.  This means that the assertion that the reference count is
zero is incorrect.  In this case, the reference count initialization
is incorrect as well and could cause arenas to be put on the free
list too early (while they still have attached threads).

	* malloc/arena.c (get_free_list): Remove assert and adjust
	reference count handling.  Add comment about reused_arena
	interaction.
	(reused_arena): Add comments abount get_free_list interaction.
	* malloc/tst-malloc-thread-exit.c: New file.
	* malloc/Makefile (tests): Add tst-malloc-thread-exit.
	(tst-malloc-thread-exit): Link against libpthread.

1 files changed, 217 insertions, 0 deletions

diff --git a/malloc/tst-malloc-thread-exit.c b/malloc/tst-malloc-thread-exit.c
new file mode 100644
index 0000000000..da7297e49c
--- /dev/null
+++ b/malloc/tst-malloc-thread-exit.c
@@ -0,0 +1,217 @@
+/* Test malloc with concurrent thread termination.
+   Copyright (C) 2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* This thread spawns a number of outer threads, equal to the arena
+   limit.  The outer threads run a loop which start and join two
+   different kinds of threads: the first kind allocates (attaching an
+   arena to the thread; malloc_first_thread) and waits, the second
+   kind waits and allocates (wait_first_threads).  Both kinds of
+   threads exit immediately after waiting.  The hope is that this will
+   exhibit races in thread termination and arena management,
+   particularly related to the arena free list.  */
+
+#include <errno.h>
+#include <pthread.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#define TIMEOUT 7
+
+static bool termination_requested;
+static int inner_thread_count = 4;
+static size_t malloc_size = 32;
+
+static void
+__attribute__ ((noinline, noclone))
+unoptimized_free (void *ptr)
+{
+  free (ptr);
+}
+
+static void *
+malloc_first_thread (void * closure)
+{
+  pthread_barrier_t *barrier = closure;
+  void *ptr = malloc (malloc_size);
+  if (ptr == NULL)
+    {
+      printf ("error: malloc: %m\n");
+      abort ();
+    }
+  int ret = pthread_barrier_wait (barrier);
+  if (ret != 0 && ret != PTHREAD_BARRIER_SERIAL_THREAD)
+    {
+      errno = ret;
+      printf ("error: pthread_barrier_wait: %m\n");
+      abort ();
+    }
+  unoptimized_free (ptr);
+  return NULL;
+}
+
+static void *
+wait_first_thread (void * closure)
+{
+  pthread_barrier_t *barrier = closure;
+  int ret = pthread_barrier_wait (barrier);
+  if (ret != 0 && ret != PTHREAD_BARRIER_SERIAL_THREAD)
+    {
+      errno = ret;
+      printf ("error: pthread_barrier_wait: %m\n");
+      abort ();
+    }
+  void *ptr = malloc (malloc_size);
+  if (ptr == NULL)
+    {
+      printf ("error: malloc: %m\n");
+      abort ();
+    }
+  unoptimized_free (ptr);
+  return NULL;
+}
+
+static void *
+outer_thread (void *closure)
+{
+  pthread_t *threads = calloc (sizeof (*threads), inner_thread_count);
+  if (threads == NULL)
+    {
+      printf ("error: calloc: %m\n");
+      abort ();
+    }
+
+  while (!__atomic_load_n (&termination_requested, __ATOMIC_RELAXED))
+    {
+      pthread_barrier_t barrier;
+      int ret = pthread_barrier_init (&barrier, NULL, inner_thread_count + 1);
+      if (ret != 0)
+        {
+          errno = ret;
+          printf ("pthread_barrier_init: %m\n");
+          abort ();
+        }
+      for (int i = 0; i < inner_thread_count; ++i)
+        {
+          void *(*func) (void *);
+          if ((i  % 2) == 0)
+            func = malloc_first_thread;
+          else
+            func = wait_first_thread;
+          ret = pthread_create (threads + i, NULL, func, &barrier);
+          if (ret != 0)
+            {
+              errno = ret;
+              printf ("error: pthread_create: %m\n");
+              abort ();
+            }
+        }
+      ret = pthread_barrier_wait (&barrier);
+      if (ret != 0 && ret != PTHREAD_BARRIER_SERIAL_THREAD)
+        {
+          errno = ret;
+          printf ("pthread_wait: %m\n");
+          abort ();
+        }
+      for (int i = 0; i < inner_thread_count; ++i)
+        {
+          ret = pthread_join (threads[i], NULL);
+          if (ret != 0)
+            {
+              ret = errno;
+              printf ("error: pthread_join: %m\n");
+              abort ();
+            }
+        }
+      ret = pthread_barrier_destroy (&barrier);
+      if (ret != 0)
+        {
+          ret = errno;
+          printf ("pthread_barrier_destroy: %m\n");
+          abort ();
+        }
+    }
+
+  free (threads);
+
+  return NULL;
+}
+
+static int
+do_test (void)
+{
+  /* The number of top-level threads should be equal to the number of
+     arenas.  See arena_get2.  */
+  long outer_thread_count = sysconf (_SC_NPROCESSORS_ONLN);
+  if (outer_thread_count >= 1)
+    {
+      /* See NARENAS_FROM_NCORES in malloc.c.  */
+      if (sizeof (long) == 4)
+        outer_thread_count *= 2;
+      else
+        outer_thread_count *= 8;
+    }
+
+  /* Leave some room for shutting down all threads gracefully.  */
+  int timeout = TIMEOUT - 2;
+
+  pthread_t *threads = calloc (sizeof (*threads), outer_thread_count);
+  if (threads == NULL)
+    {
+      printf ("error: calloc: %m\n");
+      abort ();
+    }
+
+  for (long i = 0; i < outer_thread_count; ++i)
+    {
+      int ret = pthread_create (threads + i, NULL, outer_thread, NULL);
+      if (ret != 0)
+        {
+          errno = ret;
+          printf ("error: pthread_create: %m\n");
+          abort ();
+        }
+    }
+
+  struct timespec ts = {timeout, 0};
+  if (nanosleep (&ts, NULL))
+    {
+      printf ("error: error: nanosleep: %m\n");
+      abort ();
+    }
+
+  __atomic_store_n (&termination_requested, true, __ATOMIC_RELAXED);
+
+  for (long i = 0; i < outer_thread_count; ++i)
+    {
+      int ret = pthread_join (threads[i], NULL);
+      if (ret != 0)
+        {
+          errno = ret;
+          printf ("error: pthread_join: %m\n");
+          abort ();
+        }
+    }
+  free (threads);
+
+  return 0;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"