#include "pthread_impl.h"
#include "stdio_impl.h"
#include "libc.h"
+#include "lock.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, __pthread_tsd_run_dtors);
weak_alias(dummy_0, __do_orphaned_stdio_locks);
weak_alias(dummy_0, __dl_thread_cleanup);
+weak_alias(dummy_0, __membarrier_init);
+
+static int tl_lock_count;
+static int tl_lock_waiters;
+
+void __tl_lock(void)
+{
+ int tid = __pthread_self()->tid;
+ int val = __thread_list_lock;
+ if (val == tid) {
+ tl_lock_count++;
+ return;
+ }
+ while ((val = a_cas(&__thread_list_lock, 0, tid)))
+ __wait(&__thread_list_lock, &tl_lock_waiters, val, 0);
+}
+
+void __tl_unlock(void)
+{
+ if (tl_lock_count) {
+ tl_lock_count--;
+ return;
+ }
+ a_store(&__thread_list_lock, 0);
+ if (tl_lock_waiters) __wake(&__thread_list_lock, 1, 0);
+}
+
+void __tl_sync(pthread_t td)
+{
+ a_barrier();
+ int val = __thread_list_lock;
+ if (!val) return;
+ __wait(&__thread_list_lock, &tl_lock_waiters, val, 0);
+ if (tl_lock_waiters) __wake(&__thread_list_lock, 1, 0);
+}
_Noreturn void __pthread_exit(void *result)
{
* joinable threads it's a valid usage that must be handled. */
LOCK(self->killlock);
- /* 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);
-
- /* 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, restore the tid, 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;
- UNLOCK(self->killlock);
+ /* The thread list lock must be AS-safe, and thus requires
+ * application signals to be blocked before it can be taken. */
+ __block_app_sigs(&set);
+ __tl_lock();
+
+ /* If this is the only thread in the list, don't proceed with
+ * termination of the thread, but restore the previous lock and
+ * signal state to prepare for exit to call atexit handlers. */
+ if (self->next == self) {
+ __tl_unlock();
__restore_sigs(&set);
+ UNLOCK(self->killlock);
exit(0);
}
+ /* At this point we are committed to thread termination. */
+
/* 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. */
__do_orphaned_stdio_locks();
__dl_thread_cleanup();
+ /* Last, unlink thread from the list. This change will not be visible
+ * until the lock is released, which only happens after SYS_exit
+ * has been called, via the exit futex address pointing at the lock.
+ * This needs to happen after any possible calls to LOCK() that might
+ * skip locking if libc.threads_minus_1 is zero. */
+ libc.threads_minus_1--;
+ self->next->prev = self->prev;
+ self->prev->next = self->next;
+ self->prev = self->next = self;
+
/* This atomic potentially competes with a concurrent pthread_detach
* call; the loser is responsible for freeing thread resources. */
int state = a_cas(&self->detach_state, DT_JOINABLE, DT_EXITING);
- if (state>=DT_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, we need to clear it here. */
- if (state == DT_DYNAMIC) __syscall(SYS_set_tid_address, 0);
+ if (state==DT_DETACHED && self->map_base) {
+ /* Detached threads must block even implementation-internal
+ * signals, since they will not have a stack in their last
+ * moments of existence. */
+ __block_all_sigs(&set);
/* Robust list will no longer be valid, and was already
* processed above, so unregister it with the kernel. */
__unmapself(self->map_base, self->map_size);
}
+ /* Wake any joiner. */
+ __wake(&self->detach_state, 1, 1);
+
/* After the kernel thread exits, its tid may be reused. Clear it
* to prevent inadvertent use and inform functions that would use
* it that it's no longer available. */
__pthread_self()->cancelbuf = cb->__next;
}
+struct start_args {
+ void *(*start_func)(void *);
+ void *start_arg;
+ volatile int control;
+ unsigned long sig_mask[_NSIG/8/sizeof(long)];
+};
+
static int start(void *p)
{
- pthread_t self = p;
- /* States for startlock:
- * 0 = no need for start sync
- * 1 = waiting for parent to do work
- * 2 = failure in parent, child must abort
- * 3 = success in parent, child must restore sigmask */
- if (self->startlock[0]) {
- __wait(self->startlock, 0, 1, 1);
- if (self->startlock[0] == 2) {
- self->detach_state = DT_DYNAMIC;
- pthread_exit(0);
+ struct start_args *args = p;
+ int state = args->control;
+ if (state) {
+ if (a_cas(&args->control, 1, 2)==1)
+ __wait(&args->control, 0, 2, 1);
+ if (args->control) {
+ __syscall(SYS_set_tid_address, &args->control);
+ for (;;) __syscall(SYS_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));
+ __syscall(SYS_rt_sigprocmask, SIG_SETMASK, &args->sig_mask, 0, _NSIG/8);
+ __pthread_exit(args->start_func(args->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));
+ struct start_args *args = p;
+ int (*start)(void*) = (int(*)(void*)) args->start_func;
+ __pthread_exit((void *)(uintptr_t)start(args->start_arg));
return 0;
}
static void *dummy_tsd[1] = { 0 };
weak_alias(dummy_tsd, __pthread_tsd_main);
-volatile int __block_new_threads = 0;
-size_t __default_stacksize = DEFAULT_STACK_SIZE;
-size_t __default_guardsize = DEFAULT_GUARD_SIZE;
-
static FILE *volatile dummy_file = 0;
weak_alias(dummy_file, __stdin_used);
weak_alias(dummy_file, __stdout_used);
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);
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 };
+ sigset_t set;
if (!libc.can_do_threads) return ENOSYS;
self = __pthread_self();
init_file_lock(__stderr_used);
__syscall(SYS_rt_sigprocmask, SIG_UNBLOCK, SIGPT_SET, 0, _NSIG/8);
self->tsd = (void **)__pthread_tsd_main;
+ __membarrier_init();
libc.threaded = 1;
}
if (attrp && !c11) attr = *attrp;
attr._a_guardsize = __default_guardsize;
}
- 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;
new->stack = stack;
new->stack_size = stack - stack_limit;
new->guard_size = guard;
- new->start = entry;
- new->start_arg = arg;
new->self = new;
new->tsd = (void *)tsd;
new->locale = &libc.global_locale;
if (attr._a_detach) {
new->detach_state = DT_DETACHED;
- flags -= CLONE_CHILD_CLEARTID;
} else {
new->detach_state = DT_JOINABLE;
}
- 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;
+ new->sysinfo = self->sysinfo;
+
+ /* Setup argument structure for the new thread on its stack.
+ * It's safe to access from the caller only until the thread
+ * list is unlocked. */
+ stack -= (uintptr_t)stack % sizeof(uintptr_t);
+ stack -= sizeof(struct start_args);
+ struct start_args *args = (void *)stack;
+ args->start_func = entry;
+ args->start_arg = arg;
+ args->control = attr._a_sched ? 1 : 0;
+
+ /* Application signals (but not the synccall signal) must be
+ * blocked before the thread list lock can be taken, to ensure
+ * that the lock is AS-safe. */
+ __block_app_sigs(&set);
+
+ /* Ensure SIGCANCEL is unblocked in new thread. This requires
+ * working with a copy of the set so we can restore the
+ * original mask in the calling thread. */
+ memcpy(&args->sig_mask, &set, sizeof args->sig_mask);
+ args->sig_mask[(SIGCANCEL-1)/8/sizeof(long)] &=
+ ~(1UL<<((SIGCANCEL-1)%(8*sizeof(long))));
+
+ __tl_lock();
+ libc.threads_minus_1++;
+ ret = __clone((c11 ? start_c11 : start), stack, flags, args, &new->tid, TP_ADJ(new), &__thread_list_lock);
+
+ /* All clone failures translate to EAGAIN. If explicit scheduling
+ * was requested, attempt it before unlocking the thread list so
+ * that the failed thread is never exposed and so that we can
+ * clean up all transient resource usage before returning. */
+ if (ret < 0) {
+ ret = -EAGAIN;
+ } else if (attr._a_sched) {
+ ret = __syscall(SYS_sched_setscheduler,
+ new->tid, attr._a_policy, &attr._a_prio);
+ if (a_swap(&args->control, ret ? 3 : 0)==2)
+ __wake(&args->control, 1, 1);
+ if (ret)
+ __wait(&args->control, 0, 3, 0);
+ }
- a_inc(&libc.threads_minus_1);
- ret = __clone((c11 ? start_c11 : start), stack, flags, new, &new->tid, TP_ADJ(new), &new->detach_state);
-
- __release_ptc();
-
- if (do_sched) {
- __restore_sigs(new->sigmask);
+ if (ret >= 0) {
+ new->next = self->next;
+ new->prev = self;
+ new->next->prev = new;
+ new->prev->next = new;
+ } else {
+ libc.threads_minus_1--;
}
+ __tl_unlock();
+ __restore_sigs(&set);
+ __release_ptc();
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 : 3);
- __wake(new->startlock, 1, 1);
- if (ret < 0) return -ret;
+ return -ret;
}
*res = new;
projects / musl / blobdiff