Hi Jaegeuk: We encounter a deadlock issue when Android is going to poweroff. Please help check. When unmounting of f2fs partition fail in Android poweroff procedure, init thread (pid = 1) invoke F2FS_IOC_SHUTDOWN ioctl with arg F2FS_GOING_DOWN_FULLSYNC. This ioctl cause down_write of a semaphore in the following call sequence: f2fs_ioc_shutdown() --> freeze_bdev() --> freeze_super() --> sb_wait_write(sb, SB_FREEZE_FS) --> ... ->percpu_down_write(). f2fs_ioc_shutdown() will later invoke f2fs_stop_discard_thread() and wait for stopping of f2fs_discard thread in the following call sequence: f2fs_ioc_shutdown() -->f2fs_stop_discard_thread() -->kthread_stop(discard_thread) --> wait_for_completion(). That is, init thread go sleep with a write semaphore. f2fs_discard thread is then waken up to process f2fs discard. However, f2fs_discard threshold may then hang because failing to get the semaphore aleady obtained by the slept init thread: issue_discard_thread() --> sb_start_intwrite() -->sb_start_write(sb, SB_FREEZE_FS) --> percpu_down_read() Light
