SM_TAILQ_FIRST
(SM_TAILQ_FIRST(head) == SM_TAILQ_END(head))
for((var) = SM_TAILQ_FIRST(head); \
Mon_cur_ctx = SM_TAILQ_FIRST(&Mon_ctx_head);
ctx = SM_TAILQ_FIRST(&WRK_CTX_HEAD);
ctx = SM_TAILQ_FIRST(&WRK_CTX_HEAD);