nptl/tst-create-detached.c

   1 /* Bug 20116: Test rapid creation of detached threads.
   2    Copyright (C) 2017 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If
  17    not, see <http://www.gnu.org/licenses/>.  */
  18
  19 /* The goal of the test is to trigger a failure if the parent touches
  20    any part of the thread descriptor after the detached thread has
  21    exited.  We test this by creating many detached threads with large
  22    stacks.  The stacks quickly fill the the stack cache and subsequent
  23    threads will start to cause the thread stacks to be immediately
  24    unmapped to satisfy the stack cache max.  With the stacks being
  25    unmapped the parent's read of any part of the thread descriptor will
  26    trigger a segfault.  That segfault is what we are trying to cause,
  27    since any segfault is a defect in the implementation.  */
  28
  29 #include <pthread.h>
  30 #include <stdio.h>
  31 #include <errno.h>
  32 #include <unistd.h>
  33 #include <stdbool.h>
  34 #include <sys/resource.h>
  35 #include <support/xthread.h>
  36
  37 /* Number of threads to create.  */
  38 enum { threads_to_create = 100000 };
  39
  40 /* Number of threads which should spawn other threads.  */
  41 enum { creator_threads  = 2 };
  42
  43 /* Counter of threads created so far.  This is incremented by all the
  44    running creator threads.  */
  45 static unsigned threads_created;
  46
  47 /* Thread callback which does nothing, so that the thread exits
  48    immediatedly.  */
  49 static void *
  50 do_nothing (void *arg)
  51 {
  52   return NULL;
  53 }
  54
  55 /* Attribute indicating that the thread should be created in a detached
  56    fashion.  */
  57 static pthread_attr_t detached;
  58
  59 /* Barrier to synchronize initialization.  */
  60 static pthread_barrier_t barrier;
  61
  62 static void *
  63 creator_thread (void *arg)
  64 {
  65   int ret;
  66   xpthread_barrier_wait (&barrier);
  67
  68   while (true)
  69     {
  70       pthread_t thr;
  71       /* Thread creation will fail if the kernel does not free old
  72          threads quickly enough, so we do not report errors.  */
  73       ret = pthread_create (&thr, &detached, do_nothing, NULL);
  74       if (ret == 0 && __atomic_add_fetch (&threads_created, 1, __ATOMIC_SEQ_CST)
  75           >= threads_to_create)
  76         break;
  77     }
  78
  79   return NULL;
  80 }
  81
  82 static int
  83 do_test (void)
  84 {
  85   /* Limit the size of the process, so that memory allocation will
  86      fail without impacting the entire system.  */
  87   {
  88     struct rlimit limit;
  89     if (getrlimit (RLIMIT_AS, &limit) != 0)
  90       {
  91         printf ("FAIL: getrlimit (RLIMIT_AS) failed: %m\n");
  92         return 1;
  93       }
  94     /* This limit, 800MB, is just a heuristic. Any value can be
  95        picked.  */
  96     long target = 800 * 1024 * 1024;
  97     if (limit.rlim_cur == RLIM_INFINITY || limit.rlim_cur > target)
  98       {
  99         limit.rlim_cur = target;
 100         if (setrlimit (RLIMIT_AS, &limit) != 0)
 101           {
 102             printf ("FAIL: setrlimit (RLIMIT_AS) failed: %m\n");
 103             return 1;
 104           }
 105       }
 106   }
 107
 108   xpthread_attr_init (&detached);
 109
 110   xpthread_attr_setdetachstate (&detached, PTHREAD_CREATE_DETACHED);
 111
 112   /* A large thread stack seems beneficial for reproducing a race
 113      condition in detached thread creation.  The goal is to reach the
 114      limit of the runtime thread stack cache such that the detached
 115      thread's stack is unmapped after exit and causes a segfault when
 116      the parent reads the thread descriptor data stored on the the
 117      unmapped stack.  */
 118   xpthread_attr_setstacksize (&detached, 16 * 1024 * 1024);
 119
 120   xpthread_barrier_init (&barrier, NULL, creator_threads);
 121
 122   pthread_t threads[creator_threads];
 123
 124   for (int i = 0; i < creator_threads; ++i)
 125     threads[i] = xpthread_create (NULL, creator_thread, NULL);
 126
 127   for (int i = 0; i < creator_threads; ++i)
 128     xpthread_join (threads[i]);
 129
 130   xpthread_attr_destroy (&detached);
 131
 132   xpthread_barrier_destroy (&barrier);
 133
 134   return 0;
 135 }
 136
 137 #include <support/test-driver.c>