Re: raid6 rebuild not starting

[NeilBrown <neilb@suse.de>]

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On Mon, 12 Dec 2011 08:02:33 +0200 Anssi Hannula <anssi.hannula@iki.fi> wrote:

> On Mon, Dec 12, 2011 at 7:42 AM, NeilBrown <neilb@suse.de> wrote:
> > On Mon, 12 Dec 2011 07:22:17 +0200 Anssi Hannula <anssi.hannula@iki.fi> wrote:
> >
> >> On Mon, Dec 12, 2011 at 5:01 AM, NeilBrown <neilb@suse.de> wrote:
> >> > On Sun, 11 Dec 2011 09:03:14 +0200 Anssi Hannula <anssi.hannula@iki.fi> wrote:
> >> >
> >> >> Hi!
> >> >>
> >> >> After I rebooted during a raid6 rebuild, the rebuild didn't start again.
> >> >> Instead, there is a flood of "RAID conf printout"s that seemingly happen
> >> >> on array activity.
> >> >>
> >> >> All the devices show up properly in --detail and two devices are marked
> >> >> as "spare rebuilding", and I can access the contents of the array just
> >> >> fine, but the rebuild doesn't actually start. Is this a bug or am I
> >> >> missing something? :)
> >> >>
> >> >> I was initially on 2.6.38.8, but also tried 3.1.4 which seems to have
> >> >> the same issue. mdadm is 3.1.5.
> >> >>
> >> >> I'm not using start_ro and writing to the array doesn't trigger a
> >> >> rebuild either.
> >> >>
> >> >> Attached are --examine outputs before assembly, kernel log output on
> >> >> assembly, /proc/mdstat and --detail after assembly (on 3.1.4).
> >> >>
> >> >
> >> > Thank you for the very detailed problem report.
> >>
> >> Thanks for the quick response :)
> >>
> >> > Unfortunately it is a complete mystery to me what is happening.
> >> >
> >> > The repeated "RAID conf printout" messages are almost certainly coming from
> >> > the end of raid5_remove_disk.
> >> > It is being called from remove_and_add_spares for each of the two devices
> >> > that are being rebuilt.  raid5_remove_disk declines to remove them because it
> >> > can keep rebuilding them.
> >> >
> >> > remove_and_add_spares then counts them and notes there are 2.
> >> > md_check_recovery notes that this is > 0, so it should create a thread to run
> >> > md_do_sync.
> >> >
> >> > md_do_sync should then print out a message like
> >> >  md: recovery of RAID array md0
> >> >
> >> > but it doesn't.  So something went wrong.
> >> > There are three reasons that md_do_sync might not print a message:
> >> >
> >> > 1/ MD_RECOVERY_DONE is set.  As only md_do_sync ever sets it, that is
> >> >    unlikely, and in any case md_check_recovery clears it.
> >> > 2/ mddev->ro != 0.  It is only ever set to 0, 1, or 2.  If it is 1 or 2
> >> >   then we would be able to see that in /proc/mdstat as a "(readonly)"
> >> >   status.  But we don't.
> >> > 3/ MD_RECOVERY_INTR is set. Again, md_check_recovery clears this.  It does
> >> >   get set if kthread_should_stop() returns 'true', but that should only
> >> >   happen if kthread_stop() was called.  That is only called by
> >> >   md_unregister_thread and I cannot see any way that could be call.
> >> >
> >> > So.  No idea.
> >> >
> >> > Are you compiling these kernels yourself?
> >>
> >> Nope (used Mageia kernels), but I did now (3.1.5).
> >>
> >> > If so, could you:
> >> >  - put a printk in the top of md_do_sync to report the values of
> >> >   mddev->recovery and mddev->ro
> >> >  - print a message whenever md_unregister_thread is called
> >> >  - in md_check_recovery, in the
> >> >                if (mddev->ro) {
> >> >                        /* Only thing we do on a ro array is remove
> >> >                         * failed devices.
> >> >                         */
> >> >                        mdk_rdev_t *rdev;
> >> >
> >> >  in statement, print the value of mddev->ro.
> >> >
> >> > Then see which of those printk's fire, and what they tell us.
> >>
> >> Only the last one does, and mddev->ro == 0.
> >>
> >> For reference, attached is the used patch and resulting log output.
> >>
> >
> > Thanks.
> >
> > So it isn't running md_do_sync at all. Odd.
> >
> > Could please add:
> >  - call "WARN_ON(1);" in print_raid5_conf() so we get a stack trace and can
> >    see who is calling it.
> >  - print the value that remove_and_add_spares is going to return.
> 
> Attached. As you can see, remove_and_add_spare returns 0.
> 
> --
> Anssi Hannula


Please add:

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 5c95ccb..fa56ac5 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -7328,8 +7328,10 @@ static int remove_and_add_spares(mddev_t *mddev)
 			}
 		}
 
+	printk("degraded=%d\n", mddev->degraded);
 	if (mddev->degraded) {
 		list_for_each_entry(rdev, &mddev->disks, same_set) {
+			printk("raid_disk=%d flags=%x\n", rdev->raid_disk, rdev->flags);
 			if (rdev->raid_disk >= 0 &&
 			    !test_bit(In_sync, &rdev->flags) &&
 			    !test_bit(Faulty, &rdev->flags))


'degraded' must be 2 as dmesg contains

[   45.544806] md/raid:md0: raid level 6 active with 8 out of 10 devices, algorithm 2

and 'degraded' is exactly the difference between '8' and '10' there.

raid disks 3 and 7 must have In_sync and Faulty clear as both of them just
show "spare rebuilding" in the 'detail' output.

so remove_and_add_spares "must" return 2.

Hopefully the above patch will help me understand which of those is wrong.

NeilBrown

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