1/* Copyright (C) 2004-2021 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contribute by Ulrich Drepper <drepper@redhat.com>, 2004.
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; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include <assert.h>
20#include <errno.h>
21#include <fcntl.h>
22#include <mqueue.h>
23#include <pthread.h>
24#include <signal.h>
25#include <stdlib.h>
26#include <string.h>
27#include <sysdep.h>
28#include <unistd.h>
29#include <sys/socket.h>
30#include <not-cancel.h>
31#include <nptl/pthreadP.h>
32
33
34/* Defined in the kernel headers: */
35#define NOTIFY_COOKIE_LEN 32 /* Length of the cookie used. */
36#define NOTIFY_WOKENUP 1 /* Code for notifcation. */
37#define NOTIFY_REMOVED 2 /* Code for closed message queue
38 of de-notifcation. */
39
40
41/* Data structure for the queued notification requests. */
42union notify_data
43{
44 struct
45 {
46 void (*fct) (union sigval); /* The function to run. */
47 union sigval param; /* The parameter to pass. */
48 pthread_attr_t *attr; /* Attributes to create the thread with. */
49 /* NB: on 64-bit machines the struct as a size of 24 bytes. Which means
50 byte 31 can still be used for returning the status. */
51 };
52 char raw[NOTIFY_COOKIE_LEN];
53};
54
55
56/* Keep track of the initialization. */
57static pthread_once_t once = PTHREAD_ONCE_INIT;
58
59
60/* The netlink socket. */
61static int netlink_socket = -1;
62
63
64/* Barrier used to make sure data passed to the new thread is not
65 resused by the parent. */
66static pthread_barrier_t notify_barrier;
67
68
69/* Modify the signal mask. We move this into a separate function so
70 that the stack space needed for sigset_t is not deducted from what
71 the thread can use. */
72static int
73__attribute__ ((noinline))
74change_sigmask (int how, sigset_t *oss)
75{
76 sigset_t ss;
77 sigfillset (&ss);
78 return pthread_sigmask (how, &ss, oss);
79}
80
81
82/* The function used for the notification. */
83static void *
84notification_function (void *arg)
85{
86 /* Copy the function and parameter so that the parent thread can go
87 on with its life. */
88 volatile union notify_data *data = (volatile union notify_data *) arg;
89 void (*fct) (union sigval) = data->fct;
90 union sigval param = data->param;
91
92 /* Let the parent go. */
93 (void) __pthread_barrier_wait (&notify_barrier);
94
95 /* Make the thread detached. */
96 (void) pthread_detach (pthread_self ());
97
98 /* The parent thread has all signals blocked. This is probably a
99 bit surprising for this thread. So we unblock all of them. */
100 (void) change_sigmask (SIG_UNBLOCK, NULL);
101
102 /* Now run the user code. */
103 fct (param);
104
105 /* And we are done. */
106 return NULL;
107}
108
109
110/* Helper thread. */
111static void *
112helper_thread (void *arg)
113{
114 while (1)
115 {
116 union notify_data data;
117
118 ssize_t n = __recv (netlink_socket, &data, sizeof (data),
119 MSG_NOSIGNAL | MSG_WAITALL);
120 if (n < NOTIFY_COOKIE_LEN)
121 continue;
122
123 if (data.raw[NOTIFY_COOKIE_LEN - 1] == NOTIFY_WOKENUP)
124 {
125 /* Just create the thread as instructed. There is no way to
126 report a problem with creating a thread. */
127 pthread_t th;
128 if (__builtin_expect (pthread_create (&th, data.attr,
129 notification_function, &data)
130 == 0, 0))
131 /* Since we passed a pointer to DATA to the new thread we have
132 to wait until it is done with it. */
133 (void) __pthread_barrier_wait (&notify_barrier);
134 }
135 else if (data.raw[NOTIFY_COOKIE_LEN - 1] == NOTIFY_REMOVED)
136 /* The only state we keep is the copy of the thread attributes. */
137 free (data.attr);
138 }
139 return NULL;
140}
141
142
143static void
144reset_once (void)
145{
146 once = PTHREAD_ONCE_INIT;
147}
148
149
150static void
151init_mq_netlink (void)
152{
153 /* This code might be called a second time after fork(). The file
154 descriptor is inherited from the parent. */
155 if (netlink_socket == -1)
156 {
157 /* Just a normal netlink socket, not bound. */
158 netlink_socket = __socket (AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, 0);
159 /* No need to do more if we have no socket. */
160 if (netlink_socket == -1)
161 return;
162 }
163
164 int err = 1;
165
166 /* Initialize the barrier. */
167 if (__builtin_expect (__pthread_barrier_init (&notify_barrier, NULL, 2) == 0,
168 0))
169 {
170 /* Create the helper thread. */
171 pthread_attr_t attr;
172 (void) pthread_attr_init (&attr);
173 (void) pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED);
174 /* We do not need much stack space, the bare minimum will be enough. */
175 (void) pthread_attr_setstacksize (&attr, __pthread_get_minstack (&attr));
176
177 /* Temporarily block all signals so that the newly created
178 thread inherits the mask. */
179 sigset_t oss;
180 int have_no_oss = change_sigmask (SIG_BLOCK, &oss);
181
182 pthread_t th;
183 err = pthread_create (&th, &attr, helper_thread, NULL);
184
185 /* Reset the signal mask. */
186 if (!have_no_oss)
187 pthread_sigmask (SIG_SETMASK, &oss, NULL);
188
189 (void) pthread_attr_destroy (&attr);
190
191 if (err == 0)
192 {
193 static int added_atfork;
194
195 if (added_atfork == 0
196 && pthread_atfork (NULL, NULL, reset_once) != 0)
197 {
198 /* The child thread will call recv() which is a
199 cancellation point. */
200 (void) pthread_cancel (th);
201 err = 1;
202 }
203 else
204 added_atfork = 1;
205 }
206 }
207
208 if (err != 0)
209 {
210 __close_nocancel_nostatus (netlink_socket);
211 netlink_socket = -1;
212 }
213}
214
215
216/* Register notification upon message arrival to an empty message queue
217 MQDES. */
218int
219mq_notify (mqd_t mqdes, const struct sigevent *notification)
220{
221 /* Make sure the type is correctly defined. */
222 assert (sizeof (union notify_data) == NOTIFY_COOKIE_LEN);
223
224 /* Special treatment needed for SIGEV_THREAD. */
225 if (notification == NULL || notification->sigev_notify != SIGEV_THREAD)
226 return INLINE_SYSCALL (mq_notify, 2, mqdes, notification);
227
228 /* The kernel cannot directly start threads. This will have to be
229 done at userlevel. Since we cannot start threads from signal
230 handlers we have to create a dedicated thread which waits for
231 notifications for arriving messages and creates threads in
232 response. */
233
234 /* Initialize only once. */
235 pthread_once (&once, init_mq_netlink);
236
237 /* If we cannot create the netlink socket we cannot provide
238 SIGEV_THREAD support. */
239 if (__glibc_unlikely (netlink_socket == -1))
240 {
241 __set_errno (ENOSYS);
242 return -1;
243 }
244
245 /* Create the cookie. It will hold almost all the state. */
246 union notify_data data;
247 memset (&data, '\0', sizeof (data));
248 data.fct = notification->sigev_notify_function;
249 data.param = notification->sigev_value;
250
251 if (notification->sigev_notify_attributes != NULL)
252 {
253 /* The thread attribute has to be allocated separately. */
254 data.attr = (pthread_attr_t *) malloc (sizeof (pthread_attr_t));
255 if (data.attr == NULL)
256 return -1;
257
258 memcpy (data.attr, notification->sigev_notify_attributes,
259 sizeof (pthread_attr_t));
260 }
261
262 /* Construct the new request. */
263 struct sigevent se;
264 se.sigev_notify = SIGEV_THREAD;
265 se.sigev_signo = netlink_socket;
266 se.sigev_value.sival_ptr = &data;
267
268 /* Tell the kernel. */
269 int retval = INLINE_SYSCALL (mq_notify, 2, mqdes, &se);
270
271 /* If it failed, free the allocated memory. */
272 if (__glibc_unlikely (retval != 0))
273 free (data.attr);
274
275 return retval;
276}
277