On 10/20/2017 12:28 AM, NeilBrown wrote: > On Thu, Oct 19 2017, Artur Paszkiewicz wrote: > >> On 10/19/2017 12:36 AM, NeilBrown wrote: >>> On Wed, Oct 18 2017, Artur Paszkiewicz wrote: >>> >>>> On 10/18/2017 09:29 AM, NeilBrown wrote: >>>>> On Tue, Oct 17 2017, Shaohua Li wrote: >>>>> >>>>>> On Tue, Oct 17, 2017 at 04:04:52PM +1100, Neil Brown wrote: >>>>>>> >>>>>>> lockdep currently complains about a potential deadlock >>>>>>> with sysfs access taking reconfig_mutex, and that >>>>>>> waiting for a work queue to complete. >>>>>>> >>>>>>> The cause is inappropriate overloading of work-items >>>>>>> on work-queues. >>>>>>> >>>>>>> We currently have two work-queues: md_wq and md_misc_wq. >>>>>>> They service 5 different tasks: >>>>>>> >>>>>>> mddev->flush_work md_wq >>>>>>> mddev->event_work (for dm-raid) md_misc_wq >>>>>>> mddev->del_work (mddev_delayed_delete) md_misc_wq >>>>>>> mddev->del_work (md_start_sync) md_misc_wq >>>>>>> rdev->del_work md_misc_wq >>>>>>> >>>>>>> We need to call flush_workqueue() for md_start_sync and ->event_work >>>>>>> while holding reconfig_mutex, but mustn't hold it when >>>>>>> flushing mddev_delayed_delete or rdev->del_work. >>>>>>> >>>>>>> md_wq is a bit special as it has WQ_MEM_RECLAIM so it is >>>>>>> best to leave that alone. >>>>>>> >>>>>>> So create a new workqueue, md_del_wq, and a new work_struct, >>>>>>> mddev->sync_work, so we can keep two classes of work separate. >>>>>>> >>>>>>> md_del_wq and ->del_work are used only for destroying rdev >>>>>>> and mddev. >>>>>>> md_misc_wq is used for event_work and sync_work. >>>>>>> >>>>>>> Also document the purpose of each flush_workqueue() call. >>>>>>> >>>>>>> This removes the lockdep warning. >>>>>> >>>>>> I had the exactly same patch queued internally, >>>>> >>>>> Cool :-) >>>>> >>>>>> but the mdadm test suite still >>>>>> shows lockdep warnning. I haven't time to check further. >>>>>> >>>>> >>>>> The only other lockdep I've seen later was some ext4 thing, though I >>>>> haven't tried the full test suite. I might have a look tomorrow. >>>> >>>> I'm also seeing a lockdep warning with or without this patch, >>>> reproducible with: >>>> >>> >>> Thanks! >>> Looks like using one workqueue for mddev->del_work and rdev->del_work >>> causes problems. >>> Can you try with this addition please? >> >> It helped for that case but now there is another warning triggered by: >> >> export IMSM_NO_PLATFORM=1 # for platforms without IMSM >> mdadm -C /dev/md/imsm0 -eimsm -n4 /dev/sd[a-d] -R >> mdadm -C /dev/md/vol0 -l5 -n4 /dev/sd[a-d] -R --assume-clean >> mdadm -If sda >> mdadm -a /dev/md127 /dev/sda >> mdadm -Ss > > I tried that ... and mdmon gets a SIGSEGV. > imsm_set_disk() calls get_imsm_disk() and gets a NULL back. > It then passes the NULL to mark_failure() and that dereferences it. Interesting... I can't reproduce this. Can you show the output from mdadm -E for all disks after mdmon crashes? And maybe a debug log from mdmon? > (even worse things happen if "CREATE names=yes" appears in mdadm.conf. > I should fix that). > > I added > if (!disk) > return; > > and ran it in a loop, and got the lockdep warning. > > This patch gets rid of it for me. I need to think about it some more > before I commit to it though. This fixes the warning for me too. No other issues so far. Thanks, Artur -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
