Peter Kieser [off-list ref] writes:

FYI I ran into this problem in 3.18.22 when forcing RAID5 TRIM support 
w/ raid456.devices_handle_discard_safely on Intel DC S3500 SSDs.

Can you please be precise about the problem you experienced.
Complete kernel messages are a minimum.
Anything interesting that might have been happening at the time might
help.

Thanks,
NeilBrown