On Mon, 20 Sep 2010 20:59:29 +0100
Tim Small [off-list ref] wrote:

quoted

 unfortunately I need more that just the set of blocked tasks to diagnose the
 problem.   If you could get the result of 
         echo t > /proc/sysrq-trigger
 that might help a lot.  This might be bigger than the dmesg buffer, so you
 might try booting with 'log_buf_len=1M' just to be sure.
  

Hi Neil,

Thanks for the feedback.  I've stuck the sysrq-t output here:

http://buttersideup.com/files/md-raid1-lockup-lvm-snapshot/iodeadlock-sysrq-t.txt

Unfortunately this log is not complete.  As I suggested, you need to boot
with a larger log_buf_len  (you seem to have 128K) to get able to capture the
whole thing.

NeilBrown

... this was soon after the io to md2 stopped - md0 seems fine...

oldshoreham:~# cat /proc/mdstat
Personalities : [raid1]
md2 : active raid1 sda6[0] sdb6[1]
      404600128 blocks [2/2] [UU]
      [>....................]  resync =  0.1% (437056/404600128)
finish=343321.2min speed=19K/sec


... I also tried an older Debian 5.0.x kernel from Mar 2009, which is a
less-patched 2.6.26, and got the same results.  2.6.32 hasn't deadlocked
after 10 minutes (2.6.26 usually does within a minute of boot-up), so
I'll leave it re-syncing overnight...

Cheers!

Tim.