make thread killlock async-signal-safe for pthread_kill

[musl] / src / thread / pthread_create.c

diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index 5f49109..10f1b7d 100644 (file)
--- a/src/thread/pthread_create.c
+++ b/src/thread/pthread_create.c
@@ -72,12 +72,13 @@ _Noreturn void __pthread_exit(void *result)
        /* 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. */
+        * joinable threads it's a valid usage that must be handled.
+        * Signals must be blocked since pthread_kill must be AS-safe. */
+       __block_app_sigs(&set);
        LOCK(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);
+       /* 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
@@ -85,19 +86,12 @@ _Noreturn void __pthread_exit(void *result)
         * signal state to prepare for exit to call atexit handlers. */
        if (self->next == self) {
                __tl_unlock();
-               __restore_sigs(&set);
                UNLOCK(self->killlock);
+               __restore_sigs(&set);
                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;
+       /* 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
@@ -121,6 +115,16 @@ _Noreturn void __pthread_exit(void *result)
        __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 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;
+
        /* 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);
@@ -336,7 +340,7 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att
                ~(1UL<<((SIGCANCEL-1)%(8*sizeof(long))));
 
        __tl_lock();
-       libc.threads_minus_1++;
+       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
@@ -360,7 +364,7 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att
                new->next->prev = new;
                new->prev->next = new;
        } else {
-               libc.threads_minus_1--;
+               if (!--libc.threads_minus_1) libc.need_locks = 0;
        }
        __tl_unlock();
        __restore_sigs(&set);