musl/src/thread/mtx_unlock.c

#include <threads.h>

int __pthread_mutex_unlock(mtx_t *);

int mtx_unlock(mtx_t *mtx)
{
	/* The only cases where pthread_mutex_unlock can return an
	 * error are undefined behavior for C11 mtx_unlock, so we can
	 * assume it does not return an error and simply tail call. */
	return __pthread_mutex_unlock(mtx);
}