On 2016/4/28 22:03, Peter Zijlstra wrote: > On Thu, Apr 28, 2016 at 07:51:04PM +0800, Chao Yu wrote: >>> On Wed, Apr 27, 2016 at 09:41:48PM +0800, Chao Yu wrote: >>>> From: Chao Yu <[email protected]> >>>> >>>> The following condition can happen in a preemptible kernel, it may cause >>>> checkpointer hunging. >>>> >>>> CPU0: CPU1: >>>> - write_checkpoint >>>> - do_checkpoint >>>> - wait_on_all_pages_writeback >>>> - f2fs_write_end_io >>>> - wake_up >>>> this is last writebacked page, but >>>> no sleeper in sbi->cp_wait wait >>>> queue, wake_up is not been called. >>>> - prepare_to_wait(TASK_UNINTERRUPTIBLE) >>>> Here, current task can been preempted, >>>> but there will be no waker since last >>>> write_end_io has bypassed wake_up. So >>>> current task will sleep forever. > > But here, you should be verifying if you really should go sleep; as the > code did; it tests for !get_pages(, F2FS_WRITEBACK), and if you've just > completed that very last one, this will break out.
You mean after being preempted with TASK_UNINTERRUPTIBLE status, that task still has chance to be scheduled to check '!get_pages(, F2FS_WRITEBACK)', is that right? > >>>> - io_schedule_timeout >>>
