diff options
Diffstat (limited to 'src/thread/pthread_create.c')
| -rw-r--r-- | src/thread/pthread_create.c | 103 |
1 files changed, 73 insertions, 30 deletions
diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c index 8761381a..03cdea0a 100644 --- a/src/thread/pthread_create.c +++ b/src/thread/pthread_create.c @@ -16,6 +16,30 @@ weak_alias(dummy_0, __pthread_tsd_run_dtors); 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(); @@ -40,24 +64,30 @@ _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. 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. */ @@ -84,15 +114,11 @@ _Noreturn void __pthread_exit(void *result) * 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. */ @@ -108,6 +134,9 @@ _Noreturn void __pthread_exit(void *result) __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. */ @@ -147,7 +176,7 @@ static int start(void *p) 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); } } @@ -273,14 +302,15 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att 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; @@ -294,6 +324,9 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att 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 @@ -303,14 +336,24 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att 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; } |