1 /* $OpenBSD: select_close.c,v 1.3 2021/12/24 10:22:41 visa Exp $ */
2
3 /*
4 * Copyright (c) 2021 Visa Hankala
5 *
6 * Permission to use, copy, modify, and distribute this software for any
7 * purpose with or without fee is hereby granted, provided that the above
8 * copyright notice and this permission notice appear in all copies.
9 *
10 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
11 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
12 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
13 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
14 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
15 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
16 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
17 */
18
19 /*
20 * Test behaviour when a monitored file descriptor is closed by another thread.
21 *
22 * Note that this case is not defined by POSIX.
23 */
24
25 #include <sys/types.h>
26 #include <sys/select.h>
27 #include <sys/socket.h>
28 #include <assert.h>
29 #include <err.h>
30 #include <errno.h>
31 #include <pthread.h>
32 #include <stdio.h>
33 #include <string.h>
34 #include <unistd.h>
35
36 static int barrier[2];
37 static int sock[2];
38
39 static void *
thread_main(void * arg)40 thread_main(void *arg)
41 {
42 fd_set rfds;
43 int ret;
44 char b;
45
46 FD_ZERO(&rfds);
47 FD_SET(sock[1], &rfds);
48 ret = select(sock[1] + 1, &rfds, NULL, NULL, NULL);
49 assert(ret == 1);
50 assert(FD_ISSET(sock[1], &rfds));
51
52 /* Drain data to prevent subsequent wakeups. */
53 read(sock[1], &b, 1);
54
55 /* Sync with parent thread. */
56 write(barrier[1], "y", 1);
57 read(barrier[1], &b, 1);
58
59 FD_ZERO(&rfds);
60 FD_SET(sock[1], &rfds);
61 ret = select(sock[1] + 1, &rfds, NULL, NULL, NULL);
62 assert(ret == -1);
63 assert(errno == EBADF);
64
65 return NULL;
66 }
67
68 int
main(void)69 main(void)
70 {
71 pthread_t t;
72 int ret, saved_fd;
73 char b;
74
75 /* Enforce test timeout. */
76 alarm(10);
77
78 if (socketpair(AF_UNIX, SOCK_STREAM, 0, barrier) == -1)
79 err(1, "can't create socket pair");
80
81 if (socketpair(AF_UNIX, SOCK_STREAM, 0, sock) == -1)
82 err(1, "can't create socket pair");
83
84 ret = pthread_create(&t, NULL, thread_main, NULL);
85 if (ret != 0) {
86 fprintf(stderr, "can't start thread: %s\n", strerror(ret));
87 return 1;
88 }
89
90 /* Let the thread settle in select(). */
91 usleep(100000);
92
93 /* Awaken poll(). */
94 write(sock[0], "x", 1);
95
96 /* Wait until the thread has left select(). */
97 read(barrier[0], &b, 1);
98
99 /*
100 * Close and restore the fd that the thread has polled.
101 * This creates a pending badfd knote in the kernel.
102 */
103 saved_fd = dup(sock[1]);
104 close(sock[1]);
105 dup2(saved_fd, sock[1]);
106 close(saved_fd);
107
108 /* Let the thread continue. */
109 write(barrier[0], "x", 1);
110
111 /* Let the thread settle in select(). */
112 usleep(100000);
113
114 /* Close the fd to awaken select(). */
115 close(sock[1]);
116
117 pthread_join(t, NULL);
118
119 close(sock[0]);
120
121 return 0;
122 }
123