weak_alias(dummy_0, __do_orphaned_stdio_locks);
weak_alias(dummy_0, __dl_thread_cleanup);
+void __tl_lock(void)
+{
+ if (!a_cas(&__thread_list_lock, 0, 1)) return;
+ do {
+ a_cas(&__thread_list_lock, 1, 2);
+ __futexwait(&__thread_list_lock, 2, 0);
+ } while (a_cas(&__thread_list_lock, 0, 2));
+}
+
+void __tl_unlock(void)
+{
+ if (a_swap(&__thread_list_lock, 0)==2)
+ __wake(&__thread_list_lock, 1, 0);
+}
+
+void __tl_sync(pthread_t td)
+{
+ a_barrier();
+ if (!__thread_list_lock) return;
+ a_cas(&__thread_list_lock, 1, 2);
+ __wait(&__thread_list_lock, 0, 2, 0);
+ __wake(&__thread_list_lock, 1, 0);
+}
+
_Noreturn void __pthread_exit(void *result)
{
pthread_t self = __pthread_self();
* 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. Unlink
+ * the 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. */
+ libc.threads_minus_1--;
+ self->next->prev = self->prev;
+ self->prev->next = self->next;
+ self->prev = self->next = self;
+
/* 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. */
* 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. */
if (a_swap(args->perr, ret)==-2)
__wake(args->perr, 1, 1);
if (ret) {
- self->detach_state = DT_DYNAMIC;
+ self->detach_state = DT_DETACHED;
__pthread_exit(0);
}
}
new->locale = &libc.global_locale;
if (attr._a_detach) {
new->detach_state = DT_DETACHED;
- flags -= CLONE_CHILD_CLEARTID;
} else {
new->detach_state = DT_JOINABLE;
}
new->robust_list.head = &new->robust_list.head;
new->CANARY = self->CANARY;
- /* Setup argument structure for the new thread on its stack. */
+ /* 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->perr = 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
args->sig_mask[(SIGCANCEL-1)/8/sizeof(long)] &=
~(1UL<<((SIGCANCEL-1)%(8*sizeof(long))));
- a_inc(&libc.threads_minus_1);
- ret = __clone((c11 ? start_c11 : start), stack, flags, args, &new->tid, TP_ADJ(new), &new->detach_state);
-
+ __tl_lock();
+ libc.threads_minus_1++;
+ ret = __clone((c11 ? start_c11 : start), stack, flags, args, &new->tid, TP_ADJ(new), &__thread_list_lock);
+
+ /* If clone succeeded, new thread must be linked on the thread
+ * list before unlocking it, even if scheduling may still fail. */
+ if (ret >= 0) {
+ new->next = self->next;
+ new->prev = self;
+ new->next->prev = new;
+ new->prev->next = new;
+ }
+ __tl_unlock();
__restore_sigs(&set);
__release_ptc();
if (ret < 0) {
- a_dec(&libc.threads_minus_1);
+ libc.threads_minus_1--;
if (map) __munmap(map, size);
return EAGAIN;
}
projects / oweals / musl.git / commitdiff