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1/* Bug 20116: Test rapid creation of detached threads.
2 Copyright (C) 2017-2019 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. */
38enum { threads_to_create = 100000 };
39
40/* Number of threads which should spawn other threads. */
41enum { creator_threads = 2 };
42
43/* Counter of threads created so far. This is incremented by all the
44 running creator threads. */
45static unsigned threads_created;
46
47/* Thread callback which does nothing, so that the thread exits
48 immediatedly. */
49static void *
50do_nothing (void *arg)
51{
52 return NULL;
53}
54
55/* Attribute indicating that the thread should be created in a detached
56 fashion. */
57static pthread_attr_t detached;
58
59/* Barrier to synchronize initialization. */
60static pthread_barrier_t barrier;
61
62static void *
63creator_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
82static int
83do_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#define TIMEOUT 100
138#include <support/test-driver.c>
139

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