Re: md/raid5: report one failure scenario about growing array from mirror to level 5

[Shaohua Li <shli@kernel.org>]

On Thu, Mar 16, 2017 at 10:14:04PM +0800, Zhilong Liu wrote:
> hi, list;
> 
>   I just trace the code of the following scenarios, grow array from mirror
>   to level 5,  it would be stuck at the beginning of reshape_progress when
>   using the loop devices, the same testing steps work well via to hard disk
>   devices.  refer to the detail steps as follow.
>   Is this issue only happened on my site?
> 
> *Steps for loop devices:*
> 1). create one mirror array via to mdadm source code.
> #  cd mdadm/
> #  ./test setup
> #  ./mdadm -CR /dev/md0 --level 1 -b internal -n2 /dev/loop[0-1]
> #  dmesg -c,    clean the dmesg.
> 2). triggers the reshape_request, then it would be stuck when start
> reshape_progress.
> ... ...
> linux-x4lv:~/mdadm-test # ./mdadm --grow /dev/md0 -l5 -n3 -a /dev/loop2
> mdadm: level of /dev/md0 changed to raid5
> mdadm: added /dev/loop2
> mdadm: Need to backup 128K of critical section..
> 
> linux-x4lv:~/mdadm-test # cat /proc/mdstat
> Personalities : [raid1] [raid6] [raid5] [raid4]
> md0 : active raid5 loop2[2] loop1[1] loop0[0]
>       19968 blocks super 1.2 level 5, 64k chunk, algorithm 2 [3/3] [UUU]
>       [>....................]  reshape =  0.0% (1/19968) finish=41.5min
> speed=0K/sec
>       bitmap: 0/1 pages [0KB], 65536KB chunk
> 
> unused devices: <none>
> 
> linux-x4lv:~/mdadm-test # dmesg -c
> [111544.283359] md/raid:md0: device loop1 operational as raid disk 1
> [111544.283362] md/raid:md0: device loop0 operational as raid disk 0
> [111544.296161] md/raid:md0: raid level 5 active with 2 out of 2 devices,
> algorithm 2
> [111544.296178] md/raid456: discard support disabled due to uncertainty.
> [111544.296178] Set raid456.devices_handle_discard_safely=Y to override.
> [111544.932238] md: reshape of RAID array md0
> 
> *Steps for hard disks:*
> # ./mdadm --grow /dev/md0 -l5 -n3  -a /dev/sdd
> mdadm: level of /dev/md0 changed to raid5
> mdadm: added /dev/sdd
> mdadm: Need to backup 128K of critical section..
> 
> # cat /proc/mdstat
> Personalities : [raid1] [raid0] [raid6] [raid5] [raid4]
> md0 : active raid5 sdd[2] sdc[1] sdb[0]
>       102272 blocks super 1.2 level 5, 64k chunk, algorithm 2 [3/3] [UUU]
>       [====>................]  reshape = 22.5% (23168/102272) finish=0.5min
> speed=2316K/sec
>       bitmap: 0/1 pages [0KB], 65536KB chunk
> 
> unused devices: <none>

can't reproduce locally. does this only exist in specific mdadm/kernel version?

Thanks,
Shaohua