On Mon, Nov 30, 2015 at 8:03 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > On Wed, Nov 25, 2015 at 11:11:00PM -0800, Dan Williams wrote: >> On Wed, Nov 25, 2015 at 10:27 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: >> > On Wed, Nov 25, 2015 at 02:09:34PM -0800, Dan Williams wrote: >> >> On Wed, Nov 25, 2015 at 1:50 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: >> >> > On Wed, Nov 25, 2015 at 10:37:24AM -0800, Dan Williams wrote: >> [..] >> >> That sounds good in theory. However, in the case of xfs it is already >> >> calling xfs_force_shutdown(), >> > >> > Where? >> >> In the trace I included in the cover letter. >> >> Testing this patch set reveals that xfs needs more XFS_FORCED_SHUTDOWN >> checks, especially in the unmount path. Currently we deadlock here on >> umount after block device removal: > > What's the test case? > > From what you've said, it appears to be another manifestation where > we trying to recovery from non-fatal IO errors that are being > reported by the block device, but that is short-cutting the path > that normally does shutdown detection on metadata buffer IO > completion. > > Filesystem error handling coul dbe a lot more simple if we didnt' > have to try to guess what EIO from the block device actually means. > If device unplug triggered a shutdown, we wouldn't have to care > about retrying in many cases where we do right now because shutdown > then has clear priority of all other errors we need to handle. RIgh > tnow we just have ot guess, and there's a long history of corner > cases where we have guessed wrong.... > > I have patches to fix this particular manifestation, but until we > have have notification that devices hav ebeen unplugged and are not > coming back we're going to continue to struggle to get this right > and hence have re-occurring bugs when users pull USB drives out from > under active filesystems..... > > >> >> None of this fixes the problem of dax mappings leaking past block >> >> device remove. That can be done generically without needing per-fs >> >> code. >> > >> > No, the shutdown is intended to close the race between the device >> > being removed, the mappings being invalidated and the filesytem >> > racing creating new mappings during page faults because it doesn't >> > know the device has been unplugged until it does IO that gets some >> > error in an unrecoverable path... >> >> So you want me to grow a ->sb_shutdown() method for each fs that >> supports dax only to call unmap_mapping_range on each dax inode when >> common code could have already walked the inode list. > > No, I don't want you to implement some whacky, dax only > ->sb_shutdown method. I want a notification method to be implemented > so that each filesystem can take the necessary action it requires > when the underlying block device goes away. > > Yes, that *filesystem specific method* might involve invalidating > all the dirty inodes in the filesystem, and if there are DAX > mappings in the filesystem then invalidating them, too, but that's > something the filesystem needs to take care of because *all > filesystem shutdowns must do this*. > > Do you see the distinction there? This isn't just about device > unplug - there are lots of different triggers for a filesystem > shutdown. However, regardless of the shutdown trigger, we have to > take the same action. That is, we have to prevent all pending and > future IO from being issued to the block device, *even if the block > device is still OK*. Ah, that finally got through to me. I'll refactor this to be a ->shutdown notification with a generic unmap that a filesystem can optionally call under its own discretion. As I now see that generic functionality is just common code that an fs might optionally need/use, but it is counter productive for that to be privately triggered only by the block layer and only from an event like del_gendisk. We need it in potentially all fs shutdown paths. -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
