Abdul Haleem [off-list ref] writes:

Greeting's

Kernel Oops is seen on 4.17.0-rc7-next-20180601 kernel on a bare-metal
machine when running lvm snapshot tests on nvme disks.

Machine Type: Power 8 bare-metal
kernel : 4.17.0-rc7-next-20180601
test:  
$ pvcreate -y /dev/nvme0n1
$ vgcreate avocado_vg /dev/nvme0n1
$ lvcreate --size 1.4T --name avocado_lv avocado_vg -y
$ mkfs.ext2 /dev/avocado_vg/avocado_lv
$ lvcreate --size 1G --snapshot --name avocado_sn /dev/avocado_vg/avocado_lv -y
$ lvconvert --merge /dev/avocado_vg/avocado_sn

the last command results in Oops:

Unable to handle kernel paging request for data at address 0x000000d0
Faulting instruction address: 0xc0000000002dced4
Oops: Kernel access of bad area, sig: 11 [#1]
LE SMP NR_CPUS=2048 NUMA PowerNV
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in: dm_snapshot dm_bufio nvme bnx2x iptable_mangle
ipt_MASQUERADE iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4
nf_defrag_ipv4 xt_conntrack nf_conntrack ipt_REJECT nf_reject_ipv4
xt_tcpudp tun bridge stp llc iptable_filter dm_mirror dm_region_hash
dm_log dm_service_time vmx_crypto powernv_rng rng_core dm_multipath
kvm_hv binfmt_misc kvm nfsd ip_tables x_tables autofs4 xfs lpfc
crc_t10dif crct10dif_generic mdio nvme_fc libcrc32c nvme_fabrics
nvme_core crct10dif_common [last unloaded: nvme]
CPU: 70 PID: 157763 Comm: lvconvert Not tainted 4.17.0-rc7-next-20180601-autotest-autotest #1
NIP:  c0000000002dced4 LR: c000000000244d14 CTR: c000000000244cf0
REGS: c000001f81d6b5a0 TRAP: 0300   Not tainted  (4.17.0-rc7-next-20180601-autotest-autotest)
MSR:  900000010280b033 <SF,HV,VEC,VSX,EE,FP,ME,IR,DR,RI,LE,TM[E]>  CR: 22442444  XER: 20000000
CFAR: c000000000008934 DAR: 00000000000000d0 DSISR: 40000000 SOFTE: 0
GPR00: c000000000244d14 c000001f81d6b820 c00000000109c400 c000003c9d080180
GPR04: 0000000000000001 c000001fad510000 c000001fad510000 0000000000000001
GPR08: 0000000000000000 f000000000000000 f000000000000008 0000000000000000
GPR12: c000000000244cf0 c000001ffffc4f80 00007fffa0e31090 00007fffd9d9b470
GPR16: 0000000000000000 000000000000005c 00007fffa0e3a5b0 00007fffa0e62040
GPR20: 0000010014ad7d50 0000010014ad7d20 00007fffa0e64210 0000000000000001
GPR24: 0000000000000000 c00000000081bae0 c000001ed2461b00 d00000000f859d08
GPR28: c000003c9d080180 c000000000244d14 0000000000000001 0000000000000000
NIP [c0000000002dced4] kmem_cache_free+0x1a4/0x2b0
LR [c000000000244d14] mempool_free_slab+0x24/0x40

Are you running with slub debugging enabled?
Try booting with slub_debug=FZP

cheers