summaryrefslogtreecommitdiff
path: root/src/thread/pthread_create.c
blob: 08c5f4f8b910b9faf48293c75149cc54b144e989 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
#define _GNU_SOURCE
#include "pthread_impl.h"
#include "stdio_impl.h"
#include "libc.h"
#include <sys/mman.h>
#include <string.h>
#include <stddef.h>

void *__mmap(void *, size_t, int, int, int, off_t);
int __munmap(void *, size_t);
int __mprotect(void *, size_t, int);

static void dummy_0()
{
}
weak_alias(dummy_0, __acquire_ptc);
weak_alias(dummy_0, __release_ptc);
weak_alias(dummy_0, __pthread_tsd_run_dtors);
weak_alias(dummy_0, __do_orphaned_stdio_locks);

_Noreturn void __pthread_exit(void *result)
{
	pthread_t self = __pthread_self();
	sigset_t set;

	self->canceldisable = 1;
	self->cancelasync = 0;
	self->result = result;

	while (self->cancelbuf) {
		void (*f)(void *) = self->cancelbuf->__f;
		void *x = self->cancelbuf->__x;
		self->cancelbuf = self->cancelbuf->__next;
		f(x);
	}

	__pthread_tsd_run_dtors();

	__lock(self->exitlock);

	/* Mark this thread dead before decrementing count */
	__lock(self->killlock);
	self->dead = 1;

	/* Block all signals before decrementing the live thread count.
	 * This is important to ensure that dynamically allocated TLS
	 * is not under-allocated/over-committed, and possibly for other
	 * reasons as well. */
	__block_all_sigs(&set);

	/* Wait to unlock the kill lock, which governs functions like
	 * pthread_kill which target a thread id, until signals have
	 * been blocked. This precludes observation of the thread id
	 * as a live thread (with application code running in it) after
	 * the thread was reported dead by ESRCH being returned. */
	__unlock(self->killlock);

	/* It's impossible to determine whether this is "the last thread"
	 * until performing the atomic decrement, since multiple threads
	 * could exit at the same time. For the last thread, revert the
	 * decrement and unblock signals to give the atexit handlers and
	 * stdio cleanup code a consistent state. */
	if (a_fetch_add(&libc.threads_minus_1, -1)==0) {
		libc.threads_minus_1 = 0;
		__restore_sigs(&set);
		exit(0);
	}

	if (self->locale != &libc.global_locale) {
		a_dec(&libc.uselocale_cnt);
		if (self->locale->ctype_utf8)
			a_dec(&libc.bytelocale_cnt_minus_1);
	}

	/* Process robust list in userspace to handle non-pshared mutexes
	 * and the detached thread case where the robust list head will
	 * be invalid when the kernel would process it. */
	__vm_lock();
	volatile void *volatile *rp;
	while ((rp=self->robust_list.head) && rp != &self->robust_list.head) {
		pthread_mutex_t *m = (void *)((char *)rp
			- offsetof(pthread_mutex_t, _m_next));
		int waiters = m->_m_waiters;
		int priv = (m->_m_type & 128) ^ 128;
		self->robust_list.pending = rp;
		self->robust_list.head = *rp;
		int cont = a_swap(&m->_m_lock, self->tid|0x40000000);
		self->robust_list.pending = 0;
		if (cont < 0 || waiters)
			__wake(&m->_m_lock, 1, priv);
	}
	__vm_unlock();

	__do_orphaned_stdio_locks();

	if (self->detached && self->map_base) {
		/* Detached threads must avoid the kernel clear_child_tid
		 * feature, since the virtual address will have been
		 * unmapped and possibly already reused by a new mapping
		 * at the time the kernel would perform the write. In
		 * the case of threads that started out detached, the
		 * initial clone flags are correct, but if the thread was
		 * detached later (== 2), we need to clear it here. */
		if (self->detached == 2) __syscall(SYS_set_tid_address, 0);

		/* Robust list will no longer be valid, and was already
		 * processed above, so unregister it with the kernel. */
		if (self->robust_list.off)
			__syscall(SYS_set_robust_list, 0, 3*sizeof(long));

		/* The following call unmaps the thread's stack mapping
		 * and then exits without touching the stack. */
		__unmapself(self->map_base, self->map_size);
	}

	for (;;) __syscall(SYS_exit, 0);
}

void __do_cleanup_push(struct __ptcb *cb)
{
	if (!libc.has_thread_pointer) return;
	struct pthread *self = __pthread_self();
	cb->__next = self->cancelbuf;
	self->cancelbuf = cb;
}

void __do_cleanup_pop(struct __ptcb *cb)
{
	if (!libc.has_thread_pointer) return;
	__pthread_self()->cancelbuf = cb->__next;
}

static int start(void *p)
{
	pthread_t self = p;
	if (self->startlock[0]) {
		__wait(self->startlock, 0, 1, 1);
		if (self->startlock[0]) {
			self->detached = 2;
			pthread_exit(0);
		}
		__restore_sigs(self->sigmask);
	}
	if (self->unblock_cancel)
		__syscall(SYS_rt_sigprocmask, SIG_UNBLOCK,
			SIGPT_SET, 0, _NSIG/8);
	__pthread_exit(self->start(self->start_arg));
	return 0;
}

static int start_c11(void *p)
{
	pthread_t self = p;
	int (*start)(void*) = (int(*)(void*)) self->start;
	__pthread_exit((void *)(uintptr_t)start(self->start_arg));
	return 0;
}

#define ROUND(x) (((x)+PAGE_SIZE-1)&-PAGE_SIZE)

/* pthread_key_create.c overrides this */
static volatile size_t dummy = 0;
weak_alias(dummy, __pthread_tsd_size);
static void *dummy_tsd[1] = { 0 };
weak_alias(dummy_tsd, __pthread_tsd_main);

volatile int __block_new_threads = 0;

static FILE *volatile dummy_file = 0;
weak_alias(dummy_file, __stdin_used);
weak_alias(dummy_file, __stdout_used);
weak_alias(dummy_file, __stderr_used);

static void init_file_lock(FILE *f)
{
	if (f && f->lock<0) f->lock = 0;
}

void *__copy_tls(unsigned char *);

int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict attrp, void *(*entry)(void *), void *restrict arg)
{
	int ret, c11 = (attrp == __ATTRP_C11_THREAD);
	size_t size, guard;
	struct pthread *self, *new;
	unsigned char *map = 0, *stack = 0, *tsd = 0, *stack_limit;
	unsigned flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND
		| CLONE_THREAD | CLONE_SYSVSEM | CLONE_SETTLS
		| CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID | CLONE_DETACHED;
	int do_sched = 0;
	pthread_attr_t attr = {0};

	if (!libc.can_do_threads) return ENOSYS;
	self = __pthread_self();
	if (!libc.threaded) {
		for (FILE *f=libc.ofl_head; f; f=f->next)
			init_file_lock(f);
		init_file_lock(__stdin_used);
		init_file_lock(__stdout_used);
		init_file_lock(__stderr_used);
		__syscall(SYS_rt_sigprocmask, SIG_UNBLOCK, SIGPT_SET, 0, _NSIG/8);
		self->tsd = (void **)__pthread_tsd_main;
		libc.threaded = 1;
	}
	if (attrp && !c11) attr = *attrp;

	__acquire_ptc();
	if (__block_new_threads) __wait(&__block_new_threads, 0, 1, 1);

	if (attr._a_stackaddr) {
		size_t need = libc.tls_size + __pthread_tsd_size;
		size = attr._a_stacksize + DEFAULT_STACK_SIZE;
		stack = (void *)(attr._a_stackaddr & -16);
		stack_limit = (void *)(attr._a_stackaddr - size);
		/* Use application-provided stack for TLS only when
		 * it does not take more than ~12% or 2k of the
		 * application's stack space. */
		if (need < size/8 && need < 2048) {
			tsd = stack - __pthread_tsd_size;
			stack = tsd - libc.tls_size;
			memset(stack, 0, need);
		} else {
			size = ROUND(need);
			guard = 0;
		}
	} else {
		guard = ROUND(DEFAULT_GUARD_SIZE + attr._a_guardsize);
		size = guard + ROUND(DEFAULT_STACK_SIZE + attr._a_stacksize
			+ libc.tls_size +  __pthread_tsd_size);
	}

	if (!tsd) {
		if (guard) {
			map = __mmap(0, size, PROT_NONE, MAP_PRIVATE|MAP_ANON, -1, 0);
			if (map == MAP_FAILED) goto fail;
			if (__mprotect(map+guard, size-guard, PROT_READ|PROT_WRITE)) {
				__munmap(map, size);
				goto fail;
			}
		} else {
			map = __mmap(0, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 0);
			if (map == MAP_FAILED) goto fail;
		}
		tsd = map + size - __pthread_tsd_size;
		if (!stack) {
			stack = tsd - libc.tls_size;
			stack_limit = map + guard;
		}
	}

	new = __copy_tls(tsd - libc.tls_size);
	new->map_base = map;
	new->map_size = size;
	new->stack = stack;
	new->stack_size = stack - stack_limit;
	new->start = entry;
	new->start_arg = arg;
	new->self = new;
	new->tsd = (void *)tsd;
	new->locale = &libc.global_locale;
	if (attr._a_detach) {
		new->detached = 1;
		flags -= CLONE_CHILD_CLEARTID;
	}
	if (attr._a_sched) {
		do_sched = new->startlock[0] = 1;
		__block_app_sigs(new->sigmask);
	}
	new->robust_list.head = &new->robust_list.head;
	new->unblock_cancel = self->cancel;
	new->canary = self->canary;

	a_inc(&libc.threads_minus_1);
	ret = __clone((c11 ? start_c11 : start), stack, flags, new, &new->tid, TP_ADJ(new), &new->tid);

	__release_ptc();

	if (do_sched) {
		__restore_sigs(new->sigmask);
	}

	if (ret < 0) {
		a_dec(&libc.threads_minus_1);
		if (map) __munmap(map, size);
		return EAGAIN;
	}

	if (do_sched) {
		ret = __syscall(SYS_sched_setscheduler, new->tid,
			attr._a_policy, &attr._a_prio);
		a_store(new->startlock, ret<0 ? 2 : 0);
		__wake(new->startlock, 1, 1);
		if (ret < 0) return -ret;
	}

	*res = new;
	return 0;
fail:
	__release_ptc();
	return EAGAIN;
}

weak_alias(__pthread_exit, pthread_exit);
weak_alias(__pthread_create, pthread_create);