linux 2.6.11中worker_thread被调用的流程如下:
create_workqueue->__create_workqueue->create_workqueue_thread->kthread_create->worker_thread:
worker_thread其中有这么一段:
/* Block and flush all signals */
194 sigfillset(&blocked);
195 sigprocmask(SIG_BLOCK, &blocked, NULL);
196 flush_signals(current);
197
198 /* SIG_IGN makes children autoreap: see do_notify_parent(). */