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