1 /* Copyright (C) 2002-2023 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <https://www.gnu.org/licenses/>. */
17
18 #include <errno.h>
19 #include <signal.h>
20 #include <stdlib.h>
21 #include "pthreadP.h"
22 #include <atomic.h>
23 #include <sysdep.h>
24 #include <unistd.h>
25 #include <unwind-link.h>
26 #include <stdio.h>
27 #include <gnu/lib-names.h>
28 #include <sys/single_threaded.h>
29
30 /* For asynchronous cancellation we use a signal. */
31 static void
32 sigcancel_handler (int sig, siginfo_t *si, void *ctx)
33 {
34 /* Safety check. It would be possible to call this function for
35 other signals and send a signal from another process. This is not
36 correct and might even be a security problem. Try to catch as
37 many incorrect invocations as possible. */
38 if (sig != SIGCANCEL
39 || si->si_pid != __getpid()
40 || si->si_code != SI_TKILL)
41 return;
42
43 struct pthread *self = THREAD_SELF;
44
45 int oldval = atomic_load_relaxed (&self->cancelhandling);
46 while (1)
47 {
48 /* We are canceled now. When canceled by another thread this flag
49 is already set but if the signal is directly send (internally or
50 from another process) is has to be done here. */
51 int newval = oldval | CANCELING_BITMASK | CANCELED_BITMASK;
52
53 if (oldval == newval || (oldval & EXITING_BITMASK) != 0)
54 /* Already canceled or exiting. */
55 break;
56
57 if (atomic_compare_exchange_weak_acquire (&self->cancelhandling,
58 &oldval, newval))
59 {
60 self->result = PTHREAD_CANCELED;
61
62 /* Make sure asynchronous cancellation is still enabled. */
63 if ((oldval & CANCELTYPE_BITMASK) != 0)
64 /* Run the registered destructors and terminate the thread. */
65 __do_cancel ();
66 }
67 }
68 }
69
70 int
71 __pthread_cancel (pthread_t th)
72 {
73 volatile struct pthread *pd = (volatile struct pthread *) th;
74
75 if (pd->tid == 0)
76 /* The thread has already exited on the kernel side. Its outcome
77 (regular exit, other cancelation) has already been
78 determined. */
79 return 0;
80
81 static int init_sigcancel = 0;
82 if (atomic_load_relaxed (&init_sigcancel) == 0)
83 {
84 struct sigaction sa;
85 sa.sa_sigaction = sigcancel_handler;
86 /* The signal handle should be non-interruptible to avoid the risk of
87 spurious EINTR caused by SIGCANCEL sent to process or if
88 pthread_cancel() is called while cancellation is disabled in the
89 target thread. */
90 sa.sa_flags = SA_SIGINFO | SA_RESTART;
91 __sigemptyset (&sa.sa_mask);
92 __libc_sigaction (SIGCANCEL, &sa, NULL);
93 atomic_store_relaxed (&init_sigcancel, 1);
94 }
95
96 #ifdef SHARED
97 /* Trigger an error if libgcc_s cannot be loaded. */
98 {
99 struct unwind_link *unwind_link = __libc_unwind_link_get ();
100 if (unwind_link == NULL)
101 __libc_fatal (LIBGCC_S_SO
102 " must be installed for pthread_cancel to work\n");
103 }
104 #endif
105
106 /* Some syscalls are never restarted after being interrupted by a signal
107 handler, regardless of the use of SA_RESTART (they always fail with
108 EINTR). So pthread_cancel cannot send SIGCANCEL unless the cancellation
109 is enabled and set as asynchronous (in this case the cancellation will
110 be acted in the cancellation handler instead by the syscall wrapper).
111 Otherwise the target thread is set as 'cancelling' (CANCELING_BITMASK)
112 by atomically setting 'cancelhandling' and the cancelation will be acted
113 upon on next cancellation entrypoing in the target thread.
114
115 It also requires to atomically check if cancellation is enabled and
116 asynchronous, so both cancellation state and type are tracked on
117 'cancelhandling'. */
118
119 int result = 0;
120 int oldval = atomic_load_relaxed (&pd->cancelhandling);
121 int newval;
122 do
123 {
124 again:
125 newval = oldval | CANCELING_BITMASK | CANCELED_BITMASK;
126 if (oldval == newval)
127 break;
128
129 /* If the cancellation is handled asynchronously just send a
130 signal. We avoid this if possible since it's more
131 expensive. */
132 if (cancel_enabled_and_canceled_and_async (newval))
133 {
134 /* Mark the cancellation as "in progress". */
135 int newval2 = oldval | CANCELING_BITMASK;
136 if (!atomic_compare_exchange_weak_acquire (&pd->cancelhandling,
137 &oldval, newval2))
138 goto again;
139
140 if (pd == THREAD_SELF)
141 /* This is not merely an optimization: An application may
142 call pthread_cancel (pthread_self ()) without calling
143 pthread_create, so the signal handler may not have been
144 set up for a self-cancel. */
145 {
146 pd->result = PTHREAD_CANCELED;
147 if ((newval & CANCELTYPE_BITMASK) != 0)
148 __do_cancel ();
149 }
150 else
151 /* The cancellation handler will take care of marking the
152 thread as canceled. */
153 result = __pthread_kill_internal (th, SIGCANCEL);
154
155 break;
156 }
157
158 /* A single-threaded process should be able to kill itself, since
159 there is nothing in the POSIX specification that says that it
160 cannot. So we set multiple_threads to true so that cancellation
161 points get executed. */
162 THREAD_SETMEM (THREAD_SELF, header.multiple_threads, 1);
163 #ifndef TLS_MULTIPLE_THREADS_IN_TCB
164 __libc_single_threaded_internal = 0;
165 #endif
166 }
167 while (!atomic_compare_exchange_weak_acquire (&pd->cancelhandling, &oldval,
168 newval));
169
170 return result;
171 }
172 versioned_symbol (libc, __pthread_cancel, pthread_cancel, GLIBC_2_34);
173
174 #if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_34)
175 compat_symbol (libpthread, __pthread_cancel, pthread_cancel, GLIBC_2_0);
176 #endif
177
178 /* Ensure that the unwinder is always linked in (the __pthread_unwind
179 reference from __do_cancel is weak). Use ___pthread_unwind_next
180 (three underscores) to produce a strong reference to the same
181 file. */
182 PTHREAD_STATIC_FN_REQUIRE (___pthread_unwind_next)