1 files changed, 138 insertions, 0 deletions
diff --git a/sysdeps/pthread/tst-create-detached.c b/sysdeps/pthread/tst-create-detached.c
new file mode 100644
index 0000000000..cd79c68908
--- /dev/null
+++ b/sysdeps/pthread/tst-create-detached.c
@@ -0,0 +1,138 @@
+/* Bug 20116: Test rapid creation of detached threads.
+   Copyright (C) 2017-2020 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; see the file COPYING.LIB.  If
+   not, see <https://www.gnu.org/licenses/>.  */
+
+/* The goal of the test is to trigger a failure if the parent touches
+   any part of the thread descriptor after the detached thread has
+   exited.  We test this by creating many detached threads with large
+   stacks.  The stacks quickly fill the the stack cache and subsequent
+   threads will start to cause the thread stacks to be immediately
+   unmapped to satisfy the stack cache max.  With the stacks being
+   unmapped the parent's read of any part of the thread descriptor will
+   trigger a segfault.  That segfault is what we are trying to cause,
+   since any segfault is a defect in the implementation.  */
+
+#include <pthread.h>
+#include <stdio.h>
+#include <errno.h>
+#include <unistd.h>
+#include <stdbool.h>
+#include <sys/resource.h>
+#include <support/xthread.h>
+
+/* Number of threads to create.  */
+enum { threads_to_create = 100000 };
+
+/* Number of threads which should spawn other threads.  */
+enum { creator_threads  = 2 };
+
+/* Counter of threads created so far.  This is incremented by all the
+   running creator threads.  */
+static unsigned threads_created;
+
+/* Thread callback which does nothing, so that the thread exits
+   immediatedly.  */
+static void *
+do_nothing (void *arg)
+{
+  return NULL;
+}
+
+/* Attribute indicating that the thread should be created in a detached
+   fashion.  */
+static pthread_attr_t detached;
+
+/* Barrier to synchronize initialization.  */
+static pthread_barrier_t barrier;
+
+static void *
+creator_thread (void *arg)
+{
+  int ret;
+  xpthread_barrier_wait (&barrier);
+
+  while (true)
+    {
+      pthread_t thr;
+      /* Thread creation will fail if the kernel does not free old
+	 threads quickly enough, so we do not report errors.  */
+      ret = pthread_create (&thr, &detached, do_nothing, NULL);
+      if (ret == 0 && __atomic_add_fetch (&threads_created, 1, __ATOMIC_SEQ_CST)
+          >= threads_to_create)
+        break;
+    }
+
+  return NULL;
+}
+
+static int
+do_test (void)
+{
+  /* Limit the size of the process, so that memory allocation will
+     fail without impacting the entire system.  */
+  {
+    struct rlimit limit;
+    if (getrlimit (RLIMIT_AS, &limit) != 0)
+      {
+        printf ("FAIL: getrlimit (RLIMIT_AS) failed: %m\n");
+        return 1;
+      }
+    /* This limit, 800MB, is just a heuristic. Any value can be
+       picked.  */
+    long target = 800 * 1024 * 1024;
+    if (limit.rlim_cur == RLIM_INFINITY || limit.rlim_cur > target)
+      {
+        limit.rlim_cur = target;
+        if (setrlimit (RLIMIT_AS, &limit) != 0)
+          {
+            printf ("FAIL: setrlimit (RLIMIT_AS) failed: %m\n");
+            return 1;
+          }
+      }
+  }
+
+  xpthread_attr_init (&detached);
+
+  xpthread_attr_setdetachstate (&detached, PTHREAD_CREATE_DETACHED);
+
+  /* A large thread stack seems beneficial for reproducing a race
+     condition in detached thread creation.  The goal is to reach the
+     limit of the runtime thread stack cache such that the detached
+     thread's stack is unmapped after exit and causes a segfault when
+     the parent reads the thread descriptor data stored on the the
+     unmapped stack.  */
+  xpthread_attr_setstacksize (&detached, 16 * 1024 * 1024);
+
+  xpthread_barrier_init (&barrier, NULL, creator_threads);
+
+  pthread_t threads[creator_threads];
+
+  for (int i = 0; i < creator_threads; ++i)
+    threads[i] = xpthread_create (NULL, creator_thread, NULL);
+
+  for (int i = 0; i < creator_threads; ++i)
+    xpthread_join (threads[i]);
+
+  xpthread_attr_destroy (&detached);
+
+  xpthread_barrier_destroy (&barrier);
+
+  return 0;
+}
+
+#define TIMEOUT 100
+#include <support/test-driver.c>