X-Git-Url: http://nsz.repo.hu/git/?a=blobdiff_plain;f=src%2Fthread%2Fpthread_create.c;h=2df2e9f9d63663a8bf1589c0ddace0f7eb04753d;hb=14992d4384990d40f6d3cfb799780fb696d77762;hp=49f2f7296804be25efe16ce57f6280c66751eda9;hpb=31fb174dd295e50f7c5cf18d31fcfd5fe5a063b7;p=musl diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c index 49f2f729..2df2e9f9 100644 --- a/src/thread/pthread_create.c +++ b/src/thread/pthread_create.c @@ -19,6 +19,12 @@ weak_alias(dummy_0, __pthread_tsd_run_dtors); weak_alias(dummy_0, __do_orphaned_stdio_locks); weak_alias(dummy_0, __dl_thread_cleanup); +static void *dummy_1(void *p) +{ + return 0; +} +weak_alias(dummy_1, __start_sched); + _Noreturn void __pthread_exit(void *result) { pthread_t self = __pthread_self(); @@ -37,11 +43,11 @@ _Noreturn void __pthread_exit(void *result) __pthread_tsd_run_dtors(); - __lock(self->exitlock); - - /* Mark this thread dead before decrementing count */ - __lock(self->killlock); - self->dead = 1; + /* Access to target the exiting thread with syscalls that use + * its kernel tid is controlled by killlock. For detached threads, + * any use past this point would have undefined behavior, but for + * 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 @@ -49,20 +55,14 @@ _Noreturn void __pthread_exit(void *result) * 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. */ + * 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); __restore_sigs(&set); exit(0); } @@ -89,15 +89,19 @@ _Noreturn void __pthread_exit(void *result) __do_orphaned_stdio_locks(); __dl_thread_cleanup(); - if (self->detached && self->map_base) { + /* 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 (== 2), we need to clear it here. */ - if (self->detached == 2) __syscall(SYS_set_tid_address, 0); + * detached later, we need to clear it here. */ + if (state == DT_DYNAMIC) __syscall(SYS_set_tid_address, 0); /* Robust list will no longer be valid, and was already * processed above, so unregister it with the kernel. */ @@ -113,6 +117,12 @@ _Noreturn void __pthread_exit(void *result) __unmapself(self->map_base, self->map_size); } + /* 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. */ + self->tid = 0; + UNLOCK(self->killlock); + for (;;) __syscall(SYS_exit, 0); } @@ -131,14 +141,6 @@ void __do_cleanup_pop(struct __ptcb *cb) 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); @@ -163,8 +165,8 @@ 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; +extern size_t __default_stacksize; +extern size_t __default_guardsize; static FILE *volatile dummy_file = 0; weak_alias(dummy_file, __stdin_used); @@ -189,6 +191,7 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID | CLONE_DETACHED; int do_sched = 0; pthread_attr_t attr = { 0 }; + struct start_sched_args ssa; if (!libc.can_do_threads) return ENOSYS; self = __pthread_self(); @@ -227,8 +230,8 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att memset(stack, 0, need); } else { size = ROUND(need); - guard = 0; } + guard = 0; } else { guard = ROUND(attr._a_guardsize); size = guard + ROUND(attr._a_stacksize @@ -260,30 +263,39 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att new->map_size = size; 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->detached = 1; + 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); + do_sched = 1; + ssa.futex = -1; + ssa.start_fn = new->start; + ssa.start_arg = new->start_arg; + ssa.attr = &attr; + new->start = __start_sched; + new->start_arg = &ssa; + __block_app_sigs(&ssa.mask); } 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); + 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); + __restore_sigs(&ssa.mask); } if (ret < 0) { @@ -293,11 +305,8 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att } 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; + __futexwait(&ssa.futex, -1, 1); + if (ret) return ret; } *res = new;