X-Git-Url: http://nsz.repo.hu/git/?a=blobdiff_plain;f=src%2Fthread%2Fpthread_create.c;h=087f6206d5d64165bc54ae741e77099994ae96e0;hb=d64148a8743ad9ed0594091d2ff141b1e9334d4b;hp=49f2f7296804be25efe16ce57f6280c66751eda9;hpb=31fb174dd295e50f7c5cf18d31fcfd5fe5a063b7;p=musl diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c index 49f2f729..087f6206 100644 --- a/src/thread/pthread_create.c +++ b/src/thread/pthread_create.c @@ -2,14 +2,11 @@ #include "pthread_impl.h" #include "stdio_impl.h" #include "libc.h" +#include "lock.h" #include #include #include -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() { } @@ -18,6 +15,41 @@ weak_alias(dummy_0, __release_ptc); 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) { @@ -37,36 +69,54 @@ _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; - - /* 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; + __block_app_sigs(&set); + + /* 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) { + /* Since __unmapself bypasses the normal munmap code path, + * explicitly wait for vmlock holders first. This must be + * done before any locks are taken, to avoid lock ordering + * issues that could lead to deadlock. */ + __vm_wait(); + } + + /* 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. + * Signals must be blocked since pthread_kill must be AS-safe. */ + LOCK(self->killlock); + + /* The thread list lock must be AS-safe, and thus depends on + * application signals being blocked above. */ + __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(); + UNLOCK(self->killlock); + self->detach_state = state; __restore_sigs(&set); exit(0); } + /* At this point we are committed to thread termination. */ + + /* 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. At this point the killlock + * may be released, since functions that use it will consistently + * see the thread as having exited. Release it now so that no + * remaining locks (except thread list) are held if we end up + * resetting need_locks below. */ + self->tid = 0; + UNLOCK(self->killlock); + /* 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. */ @@ -89,30 +139,36 @@ _Noreturn void __pthread_exit(void *result) __do_orphaned_stdio_locks(); __dl_thread_cleanup(); - 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); + /* 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 process appears single-threaded. */ + if (!--libc.threads_minus_1) libc.need_locks = -1; + self->next->prev = self->prev; + self->prev->next = self->next; + self->prev = self->next = self; + + 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. */ if (self->robust_list.off) __syscall(SYS_set_robust_list, 0, 3*sizeof(long)); - /* Since __unmapself bypasses the normal munmap code path, - * explicitly wait for vmlock holders first. */ - __vm_wait(); - /* The following call unmaps the thread's stack mapping * and then exits without touching the stack. */ __unmapself(self->map_base, self->map_size); } + /* Wake any joiner. */ + a_store(&self->detach_state, DT_EXITED); + __wake(&self->detach_state, 1, 1); + for (;;) __syscall(SYS_exit, 0); } @@ -128,29 +184,35 @@ void __do_cleanup_pop(struct __ptcb *cb) __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; - if (self->startlock[0]) { - __wait(self->startlock, 0, 1, 1); - if (self->startlock[0]) { - self->detached = 2; - 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; } @@ -162,10 +224,6 @@ 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; -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); @@ -176,8 +234,6 @@ 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); @@ -187,8 +243,8 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att 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(); @@ -201,6 +257,7 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att 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; @@ -211,8 +268,6 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att 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; @@ -227,8 +282,8 @@ 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 @@ -260,44 +315,75 @@ 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->start = entry; - new->start_arg = arg; + new->guard_size = guard; 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->detach_state = DT_DETACHED; + } else { + new->detach_state = DT_JOINABLE; } 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(); + 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(); + if (!libc.threads_minus_1++) libc.need_locks = 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); + } - 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 { + if (!--libc.threads_minus_1) libc.need_locks = 0; } + __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 : 0); - __wake(new->startlock, 1, 1); - if (ret < 0) return -ret; + return -ret; } *res = new;