malloc: Add missing arena lock in malloc_info [BZ #22408]

Obtain the size information while the arena lock is acquired, and only
print it later.

malloc/tst-malloc_info.c

@@ -0,0 +1,101 @@
+/* Smoke test for malloc_info.
+   Copyright (C) 2017 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/>.  */
+
+/* The purpose of this test is to provide a quick way to run
+   malloc_info in a multi-threaded process.  */
+
+#include <array_length.h>
+#include <malloc.h>
+#include <stdlib.h>
+#include <support/support.h>
+#include <support/xthread.h>
+
+/* This barrier is used to have the main thread wait until the helper
+   threads have performed their allocations.  */
+static pthread_barrier_t barrier;
+
+enum
+  {
+    /* Number of threads performing allocations.  */
+    thread_count  = 4,
+
+    /* Amount of memory allocation per thread.  This should be large
+       enough to cause the allocation of multiple heaps per arena.  */
+    per_thread_allocations
+      = sizeof (void *) == 4 ? 16 * 1024 * 1024 : 128 * 1024 * 1024,
+  };
+
+static void *
+allocation_thread_function (void *closure)
+{
+  struct list
+  {
+    struct list *next;
+    long dummy[4];
+  };
+
+  struct list *head = NULL;
+  size_t allocated = 0;
+  while (allocated < per_thread_allocations)
+    {
+      struct list *new_head = xmalloc (sizeof (*new_head));
+      allocated += sizeof (*new_head);
+      new_head->next = head;
+      head = new_head;
+    }
+
+  xpthread_barrier_wait (&barrier);
+
+  /* Main thread prints first statistics here.  */
+
+  xpthread_barrier_wait (&barrier);
+
+  while (head != NULL)
+    {
+      struct list *next_head = head->next;
+      free (head);
+      head = next_head;
+    }
+
+  return NULL;
+}
+
+static int
+do_test (void)
+{
+  xpthread_barrier_init (&barrier, NULL, thread_count + 1);
+
+  pthread_t threads[thread_count];
+  for (size_t i = 0; i < array_length (threads); ++i)
+    threads[i] = xpthread_create (NULL, allocation_thread_function, NULL);
+
+  xpthread_barrier_wait (&barrier);
+  puts ("info: After allocation:");
+  malloc_info (0, stdout);
+
+  xpthread_barrier_wait (&barrier);
+  for (size_t i = 0; i < array_length (threads); ++i)
+    xpthread_join (threads[i]);
+
+  puts ("\ninfo: After deallocation:");
+  malloc_info (0, stdout);
+
+  return 0;
+}
+
+#include <support/test-driver.c>