pthread_create.c raw
1 #define _GNU_SOURCE
2 #include "pthread_impl.h"
3 #include "stdio_impl.h"
4 #include "libc.h"
5 #include "lock.h"
6 #include <sys/mman.h>
7 #include <string.h>
8 #include <stddef.h>
9
10 static void dummy_0()
11 {
12 }
13 weak_alias(dummy_0, __acquire_ptc);
14 weak_alias(dummy_0, __release_ptc);
15 weak_alias(dummy_0, __pthread_tsd_run_dtors);
16 weak_alias(dummy_0, __do_orphaned_stdio_locks);
17 weak_alias(dummy_0, __dl_thread_cleanup);
18 weak_alias(dummy_0, __membarrier_init);
19
20 static int tl_lock_count;
21 static int tl_lock_waiters;
22
23 void __tl_lock(void)
24 {
25 int tid = __pthread_self()->tid;
26 int val = __thread_list_lock;
27 if (val == tid) {
28 tl_lock_count++;
29 return;
30 }
31 while ((val = a_cas(&__thread_list_lock, 0, tid)))
32 __wait(&__thread_list_lock, &tl_lock_waiters, val, 0);
33 }
34
35 void __tl_unlock(void)
36 {
37 if (tl_lock_count) {
38 tl_lock_count--;
39 return;
40 }
41 a_store(&__thread_list_lock, 0);
42 if (tl_lock_waiters) __wake(&__thread_list_lock, 1, 0);
43 }
44
45 void __tl_sync(pthread_t td)
46 {
47 a_barrier();
48 int val = __thread_list_lock;
49 if (!val) return;
50 __wait(&__thread_list_lock, &tl_lock_waiters, val, 0);
51 if (tl_lock_waiters) __wake(&__thread_list_lock, 1, 0);
52 }
53
54 _Noreturn void __pthread_exit(void *result)
55 {
56 pthread_t self = __pthread_self();
57 sigset_t set;
58
59 self->canceldisable = 1;
60 self->cancelasync = 0;
61 self->result = result;
62
63 while (self->cancelbuf) {
64 void (*f)(void *) = self->cancelbuf->__f;
65 void *x = self->cancelbuf->__x;
66 self->cancelbuf = self->cancelbuf->__next;
67 f(x);
68 }
69
70 __pthread_tsd_run_dtors();
71
72 __block_app_sigs(&set);
73
74 /* This atomic potentially competes with a concurrent pthread_detach
75 * call; the loser is responsible for freeing thread resources. */
76 int state = a_cas(&self->detach_state, DT_JOINABLE, DT_EXITING);
77
78 if (state==DT_DETACHED && self->map_base) {
79 /* Since __unmapself bypasses the normal munmap code path,
80 * explicitly wait for vmlock holders first. This must be
81 * done before any locks are taken, to avoid lock ordering
82 * issues that could lead to deadlock. */
83 __vm_wait();
84 }
85
86 /* Access to target the exiting thread with syscalls that use
87 * its kernel tid is controlled by killlock. For detached threads,
88 * any use past this point would have undefined behavior, but for
89 * joinable threads it's a valid usage that must be handled.
90 * Signals must be blocked since pthread_kill must be AS-safe. */
91 LOCK(self->killlock);
92
93 /* The thread list lock must be AS-safe, and thus depends on
94 * application signals being blocked above. */
95 __tl_lock();
96
97 /* If this is the only thread in the list, don't proceed with
98 * termination of the thread, but restore the previous lock and
99 * signal state to prepare for exit to call atexit handlers. */
100 if (self->next == self) {
101 __tl_unlock();
102 UNLOCK(self->killlock);
103 self->detach_state = state;
104 __restore_sigs(&set);
105 exit(0);
106 }
107
108 /* At this point we are committed to thread termination. */
109
110 /* Process robust list in userspace to handle non-pshared mutexes
111 * and the detached thread case where the robust list head will
112 * be invalid when the kernel would process it. */
113 __vm_lock();
114 volatile void *volatile *rp;
115 while ((rp=self->robust_list.head) && rp != &self->robust_list.head) {
116 pthread_mutex_t *m = (void *)((char *)rp
117 - offsetof(pthread_mutex_t, _m_next));
118 int waiters = m->_m_waiters;
119 int priv = (m->_m_type & 128) ^ 128;
120 self->robust_list.pending = rp;
121 self->robust_list.head = *rp;
122 int cont = a_swap(&m->_m_lock, 0x40000000);
123 self->robust_list.pending = 0;
124 if (cont < 0 || waiters)
125 __wake(&m->_m_lock, 1, priv);
126 }
127 __vm_unlock();
128
129 __do_orphaned_stdio_locks();
130 __dl_thread_cleanup();
131
132 /* Last, unlink thread from the list. This change will not be visible
133 * until the lock is released, which only happens after SYS_exit
134 * has been called, via the exit futex address pointing at the lock.
135 * This needs to happen after any possible calls to LOCK() that might
136 * skip locking if process appears single-threaded. */
137 if (!--libc.threads_minus_1) libc.need_locks = -1;
138 self->next->prev = self->prev;
139 self->prev->next = self->next;
140 self->prev = self->next = self;
141
142 if (state==DT_DETACHED && self->map_base) {
143 /* Detached threads must block even implementation-internal
144 * signals, since they will not have a stack in their last
145 * moments of existence. */
146 __block_all_sigs(&set);
147
148 /* Robust list will no longer be valid, and was already
149 * processed above, so unregister it with the kernel. */
150 if (self->robust_list.off)
151 __syscall(SYS_set_robust_list, 0, 3*sizeof(long));
152
153 /* The following call unmaps the thread's stack mapping
154 * and then exits without touching the stack. */
155 __unmapself(self->map_base, self->map_size);
156 }
157
158 /* Wake any joiner. */
159 a_store(&self->detach_state, DT_EXITED);
160 __wake(&self->detach_state, 1, 1);
161
162 /* After the kernel thread exits, its tid may be reused. Clear it
163 * to prevent inadvertent use and inform functions that would use
164 * it that it's no longer available. */
165 self->tid = 0;
166 UNLOCK(self->killlock);
167
168 for (;;) __syscall(SYS_exit, 0);
169 }
170
171 void __do_cleanup_push(struct __ptcb *cb)
172 {
173 struct pthread *self = __pthread_self();
174 cb->__next = self->cancelbuf;
175 self->cancelbuf = cb;
176 }
177
178 void __do_cleanup_pop(struct __ptcb *cb)
179 {
180 __pthread_self()->cancelbuf = cb->__next;
181 }
182
183 struct start_args {
184 void *(*start_func)(void *);
185 void *start_arg;
186 volatile int control;
187 unsigned long sig_mask[_NSIG/8/sizeof(long)];
188 };
189
190 static int start(void *p)
191 {
192 struct start_args *args = p;
193 int state = args->control;
194 if (state) {
195 if (a_cas(&args->control, 1, 2)==1)
196 __wait(&args->control, 0, 2, 1);
197 if (args->control) {
198 __syscall(SYS_set_tid_address, &args->control);
199 for (;;) __syscall(SYS_exit, 0);
200 }
201 }
202 __syscall(SYS_rt_sigprocmask, SIG_SETMASK, &args->sig_mask, 0, _NSIG/8);
203 __pthread_exit(args->start_func(args->start_arg));
204 return 0;
205 }
206
207 static int start_c11(void *p)
208 {
209 struct start_args *args = p;
210 int (*start)(void*) = (int(*)(void*)) args->start_func;
211 __pthread_exit((void *)(uintptr_t)start(args->start_arg));
212 return 0;
213 }
214
215 #define ROUND(x) (((x)+PAGE_SIZE-1)&-PAGE_SIZE)
216
217 /* pthread_key_create.c overrides this */
218 static volatile size_t dummy = 0;
219 weak_alias(dummy, __pthread_tsd_size);
220 static void *dummy_tsd[1] = { 0 };
221 weak_alias(dummy_tsd, __pthread_tsd_main);
222
223 static FILE *volatile dummy_file = 0;
224 weak_alias(dummy_file, __stdin_used);
225 weak_alias(dummy_file, __stdout_used);
226 weak_alias(dummy_file, __stderr_used);
227
228 static void init_file_lock(FILE *f)
229 {
230 if (f && f->lock<0) f->lock = 0;
231 }
232
233 int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict attrp, void *(*entry)(void *), void *restrict arg)
234 {
235 int ret, c11 = (attrp == __ATTRP_C11_THREAD);
236 size_t size, guard;
237 struct pthread *self, *new;
238 unsigned char *map = 0, *stack = 0, *tsd = 0, *stack_limit;
239 unsigned flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND
240 | CLONE_THREAD | CLONE_SYSVSEM | CLONE_SETTLS
241 | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID | CLONE_DETACHED;
242 pthread_attr_t attr = { 0 };
243 sigset_t set;
244
245 if (!libc.can_do_threads) return ENOSYS;
246 self = __pthread_self();
247 if (!libc.threaded) {
248 for (FILE *f=*__ofl_lock(); f; f=f->next)
249 init_file_lock(f);
250 __ofl_unlock();
251 init_file_lock(__stdin_used);
252 init_file_lock(__stdout_used);
253 init_file_lock(__stderr_used);
254 __syscall(SYS_rt_sigprocmask, SIG_UNBLOCK, SIGPT_SET, 0, _NSIG/8);
255 self->tsd = (void **)__pthread_tsd_main;
256 __membarrier_init();
257 libc.threaded = 1;
258 }
259 if (attrp && !c11) attr = *attrp;
260
261 __acquire_ptc();
262 if (!attrp || c11) {
263 attr._a_stacksize = __default_stacksize;
264 attr._a_guardsize = __default_guardsize;
265 }
266
267 if (attr._a_stackaddr) {
268 size_t need = libc.tls_size + __pthread_tsd_size;
269 size = attr._a_stacksize;
270 stack = (void *)(attr._a_stackaddr & -16);
271 stack_limit = (void *)(attr._a_stackaddr - size);
272 /* Use application-provided stack for TLS only when
273 * it does not take more than ~12% or 2k of the
274 * application's stack space. */
275 if (need < size/8 && need < 2048) {
276 tsd = stack - __pthread_tsd_size;
277 stack = tsd - libc.tls_size;
278 memset(stack, 0, need);
279 } else {
280 size = ROUND(need);
281 }
282 guard = 0;
283 } else {
284 guard = ROUND(attr._a_guardsize);
285 size = guard + ROUND(attr._a_stacksize
286 + libc.tls_size + __pthread_tsd_size);
287 }
288
289 if (!tsd) {
290 if (guard) {
291 map = __mmap(0, size, PROT_NONE, MAP_PRIVATE|MAP_ANON, -1, 0);
292 if (map == MAP_FAILED) goto fail;
293 if (__mprotect(map+guard, size-guard, PROT_READ|PROT_WRITE)
294 && errno != ENOSYS) {
295 __munmap(map, size);
296 goto fail;
297 }
298 } else {
299 map = __mmap(0, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 0);
300 if (map == MAP_FAILED) goto fail;
301 }
302 tsd = map + size - __pthread_tsd_size;
303 if (!stack) {
304 stack = tsd - libc.tls_size;
305 stack_limit = map + guard;
306 }
307 }
308
309 new = __copy_tls(tsd - libc.tls_size);
310 new->map_base = map;
311 new->map_size = size;
312 new->stack = stack;
313 new->stack_size = stack - stack_limit;
314 new->guard_size = guard;
315 new->self = new;
316 new->tsd = (void *)tsd;
317 new->locale = &libc.global_locale;
318 if (attr._a_detach) {
319 new->detach_state = DT_DETACHED;
320 } else {
321 new->detach_state = DT_JOINABLE;
322 }
323 new->robust_list.head = &new->robust_list.head;
324 new->canary = self->canary;
325 new->sysinfo = self->sysinfo;
326
327 /* Setup argument structure for the new thread on its stack.
328 * It's safe to access from the caller only until the thread
329 * list is unlocked. */
330 stack -= (uintptr_t)stack % sizeof(uintptr_t);
331 stack -= sizeof(struct start_args);
332 struct start_args *args = (void *)stack;
333 args->start_func = entry;
334 args->start_arg = arg;
335 args->control = attr._a_sched ? 1 : 0;
336
337 /* Application signals (but not the synccall signal) must be
338 * blocked before the thread list lock can be taken, to ensure
339 * that the lock is AS-safe. */
340 __block_app_sigs(&set);
341
342 /* Ensure SIGCANCEL is unblocked in new thread. This requires
343 * working with a copy of the set so we can restore the
344 * original mask in the calling thread. */
345 memcpy(&args->sig_mask, &set, sizeof args->sig_mask);
346 args->sig_mask[(SIGCANCEL-1)/8/sizeof(long)] &=
347 ~(1UL<<((SIGCANCEL-1)%(8*sizeof(long))));
348
349 __tl_lock();
350 if (!libc.threads_minus_1++) libc.need_locks = 1;
351 ret = __clone((c11 ? start_c11 : start), stack, flags, args, &new->tid, TP_ADJ(new), &__thread_list_lock);
352
353 /* All clone failures translate to EAGAIN. If explicit scheduling
354 * was requested, attempt it before unlocking the thread list so
355 * that the failed thread is never exposed and so that we can
356 * clean up all transient resource usage before returning. */
357 if (ret < 0) {
358 ret = -EAGAIN;
359 } else if (attr._a_sched) {
360 ret = __syscall(SYS_sched_setscheduler,
361 new->tid, attr._a_policy, &attr._a_prio);
362 if (a_swap(&args->control, ret ? 3 : 0)==2)
363 __wake(&args->control, 1, 1);
364 if (ret)
365 __wait(&args->control, 0, 3, 0);
366 }
367
368 if (ret >= 0) {
369 new->next = self->next;
370 new->prev = self;
371 new->next->prev = new;
372 new->prev->next = new;
373 } else {
374 if (!--libc.threads_minus_1) libc.need_locks = 0;
375 }
376 __tl_unlock();
377 __restore_sigs(&set);
378 __release_ptc();
379
380 if (ret < 0) {
381 if (map) __munmap(map, size);
382 return -ret;
383 }
384
385 *res = new;
386 return 0;
387 fail:
388 __release_ptc();
389 return EAGAIN;
390 }
391
392 weak_alias(__pthread_exit, pthread_exit);
393 weak_alias(__pthread_create, pthread_create);
394