flush_thread
wake_up_process(wc->flush_thread);
struct task_struct *flush_thread;
if (wc->flush_thread)
kthread_stop(wc->flush_thread);
wc->flush_thread = kthread_run(writecache_flush_thread, wc, "dm_writecache_flush");
if (IS_ERR(wc->flush_thread)) {
r = PTR_ERR(wc->flush_thread);
wc->flush_thread = NULL;
flush_thread();
struct task_struct *flush_thread = fcc->f2fs_issue_flush;
kthread_stop(flush_thread);
extern void flush_thread(void);