mdadm --stop goes off and never comes back?

["Jon Nelson" <jnelson-linux-raid@jamponi.net>]

This just happened to me.
Create raid with:

mdadm --create /dev/md2 --level=raid10 --raid-devices=3
--spare-devices=0 --layout=o2 /dev/sdb3 /dev/sdc3 /dev/sdd3

cat /proc/mdstat

md2 : active raid10 sdd3[2] sdc3[1] sdb3[0]
      5855424 blocks 64K chunks 2 offset-copies [3/3] [UUU]
      [==>..................]  resync = 14.6% (859968/5855424)
finish=1.3min speed=61426K/sec

Some log messages:

Dec 18 15:02:28 turnip kernel: md: md2: raid array is not clean --
starting background reconstruction
Dec 18 15:02:28 turnip kernel: raid10: raid set md2 active with 3 out
of 3 devices
Dec 18 15:02:28 turnip kernel: md: resync of RAID array md2
Dec 18 15:02:28 turnip kernel: md: minimum _guaranteed_  speed: 1000
KB/sec/disk.
Dec 18 15:02:28 turnip kernel: md: using maximum available idle IO
bandwidth (but not more than 200000 KB/sec) for resync.
Dec 18 15:02:28 turnip kernel: md: using 128k window, over a total of
5855424 blocks.
Dec 18 15:03:36 turnip kernel: md: md2: resync done.
Dec 18 15:03:36 turnip kernel: md: checkpointing resync of md2.

I tried to stop the array:

mdadm --stop /dev/md2

and mdadm never came back. It's off in the kernel somewhere. :-(

kill, of course, has no effect.
The machine still runs fine, the rest of the raids (md0 and md1) work
fine (same disks).

The output (snipped, only mdadm) of 'echo t > /proc/sysrq-trigger'

Dec 18 15:09:13 turnip kernel: mdadm         S 0001e5359fa38fb0     0
3943      1 (NOTLB)
Dec 18 15:09:13 turnip kernel:  ffff810033e7ddc8 0000000000000086
0000000000000000 0000000000000092
Dec 18 15:09:13 turnip kernel:  0000000000000fc7 ffff810033e7dd78
ffffffff80617800 ffffffff80617800
Dec 18 15:09:13 turnip kernel:  ffffffff8061d210 ffffffff80617800
ffffffff80617800 0000000000000000
Dec 18 15:09:13 turnip kernel: Call Trace:
Dec 18 15:09:13 turnip kernel:  [<ffffffff803fac96>]
__mutex_lock_interruptible_slowpath+0x8b/0xca
Dec 18 15:09:13 turnip kernel:  [<ffffffff802acccb>] do_open+0x222/0x2a5
Dec 18 15:09:13 turnip kernel:  [<ffffffff8038705d>] md_seq_show+0x127/0x6c1
Dec 18 15:09:13 turnip kernel:  [<ffffffff80275597>] vma_merge+0x141/0x1ee
Dec 18 15:09:13 turnip kernel:  [<ffffffff802a2aa0>] seq_read+0x1bf/0x28b
Dec 18 15:09:13 turnip kernel:  [<ffffffff8028a42d>] vfs_read+0xcb/0x153
Dec 18 15:09:13 turnip kernel:  [<ffffffff8028a7c1>] sys_read+0x45/0x6e
Dec 18 15:09:13 turnip kernel:  [<ffffffff80209c2e>] system_call+0x7e/0x83



What happened? Is there any debug info I can provide before I reboot?



-- 
Jon