Hi Neil

Just wondering what the status is here - do you need any more from me or is it
on your stack?

The patch helped but didn't cure.
After a clean boot it mounted correctly first try.
Then I unmounted, stopped and re-assembled the array.
The next mount failed.
The subsequent mount succeeded.

How do other block devices initialise their partitions on 'discovery'?

David

David Greaves wrote:

Neil Brown wrote:

quoted

On Tuesday April 24, david@dgreaves.com wrote:

quoted

Neil, isn't it easy to just do this after an assemble?

Yes, but it should not be needed, and I'd like to understand why it
is.
One of the last things do_md_run does is
   mddev->changed = 1;

When you next open /dev/md_d0, md_open is called which calls
check_disk_change().
This will call into md_fops->md_media_changed which will return the
value of mddev->changed, which will be '1'.
So check_disk_change will then call md_fops->revalidate_disk which
will set mddev->changed to 0, and will then set bd_invalidated to 1
(as bd_disk->minors > 1 (being 64)).

md_open will then return into do_open (in fs/block_dev.c) and because
bd_invalidated is true, it will call rescan_partitions and the
partitions will appear.

Hmmm... there is room for a race there.  If some other process opens
/dev/md_d0 before mdadm gets to close it, it will call
rescan_partitions before first calling  bd_set_size to update the size
of the bdev.  So when we try to read the partition table, it will
appear to be reading past the EOF, and will not actually read
anything..

I guess udev must be opening the block device at exactly the wrong
time. 

I can simulate this by holding /dev/md_d0 open while assembling the
array.  If I do that, the partitions don't get created.
Yuck.

Maybe I could call bd_set_size in md_open before calling
check_disk_change..

Yep, this patch seems to fix it.  Could you confirm?

almost...

teak:~# mdadm --assemble /dev/md_d0 --auto=parts /dev/sd[bcdef]1
mdadm: /dev/md_d0 has been started with 5 drives.
teak:~# mount /media
teak:~# umount /media
teak:~# mdadm --stop /dev/md_d0
mdadm: stopped /dev/md_d0
teak:~# mdadm --assemble /dev/md_d0 --auto=parts /dev/sd[bcdef]1
mdadm: /dev/md_d0 has been started with 5 drives.
teak:~# mount /media
mount: No such file or directory
teak:~# mount /media
teak:~#
(second mount succeeds second time around)



md: md_d0 stopped.
md: bind<sdc1>
md: bind<sdd1>
md: bind<sdb1>
md: bind<sdf1>
md: bind<sde1>
raid5: device sde1 operational as raid disk 0
raid5: device sdf1 operational as raid disk 4
raid5: device sdb1 operational as raid disk 3
raid5: device sdd1 operational as raid disk 2
raid5: device sdc1 operational as raid disk 1
raid5: allocated 5236kB for md_d0
raid5: raid level 5 set md_d0 active with 5 out of 5 devices, algorithm 2
RAID5 conf printout:
 --- rd:5 wd:5
 disk 0, o:1, dev:sde1
 disk 1, o:1, dev:sdc1
 disk 2, o:1, dev:sdd1
 disk 3, o:1, dev:sdb1
 disk 4, o:1, dev:sdf1
md_d0: bitmap initialized from disk: read 1/1 pages, set 0 bits, status: 0
created bitmap (10 pages) for device md_d0
 md_d0: p1 p2
Filesystem "md_d0p1": Disabling barriers, not supported with external log device
XFS mounting filesystem md_d0p1
Ending clean XFS mount for filesystem: md_d0p1
md: md_d0 stopped.
md: unbind<sde1>
md: export_rdev(sde1)
md: unbind<sdf1>
md: export_rdev(sdf1)
md: unbind<sdb1>
md: export_rdev(sdb1)
md: unbind<sdd1>
md: export_rdev(sdd1)
md: unbind<sdc1>
md: export_rdev(sdc1)
md: md_d0 stopped.
md: bind<sdc1>
md: bind<sdd1>
md: bind<sdb1>
md: bind<sdf1>
md: bind<sde1>
raid5: device sde1 operational as raid disk 0
raid5: device sdf1 operational as raid disk 4
raid5: device sdb1 operational as raid disk 3
raid5: device sdd1 operational as raid disk 2
raid5: device sdc1 operational as raid disk 1
raid5: allocated 5236kB for md_d0
raid5: raid level 5 set md_d0 active with 5 out of 5 devices, algorithm 2
RAID5 conf printout:
 --- rd:5 wd:5
 disk 0, o:1, dev:sde1
 disk 1, o:1, dev:sdc1
 disk 2, o:1, dev:sdd1
 disk 3, o:1, dev:sdb1
 disk 4, o:1, dev:sdf1
md_d0: bitmap initialized from disk: read 1/1 pages, set 0 bits, status: 0
created bitmap (10 pages) for device md_d0
 md_d0: p1 p2
XFS: Invalid device [/dev/md_d0p2], error=-2
Filesystem "md_d0p1": Disabling barriers, not supported with external log device
XFS mounting filesystem md_d0p1
Ending clean XFS mount for filesystem: md_d0p1


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