1. Please describe the problem:
Panic running CKI blktests [1].

[ 6180.774621] run blktests block/006 at 2021-08-16 11:36:20 
[ 6180.811264] null_blk: module loaded 
[ 6183.830485] Unable to handle kernel NULL pointer dereference at virtual address 00000000000002b8 
[ 6183.839284] Mem abort info: 
[ 6183.842066]   ESR = 0x96000004 
[ 6183.845122]   EC = 0x25: DABT (current EL), IL = 32 bits 
[ 6183.850423]   SET = 0, FnV = 0 
[ 6183.853465]   EA = 0, S1PTW = 0 
[ 6183.856600]   FSC = 0x04: level 0 translation fault 
[ 6183.861466] Data abort info: 
[ 6183.864335]   ISV = 0, ISS = 0x00000004 
[ 6183.868165]   CM = 0, WnR = 0 
[ 6183.871121] user pgtable: 4k pages, 48-bit VAs, pgdp=00004000319bd000 
[ 6183.877558] [00000000000002b8] pgd=0000000000000000, p4d=0000000000000000 
[ 6183.884342] Internal error: Oops: 96000004 [#1] SMP 
[ 6183.889214] Modules linked in: null_blk af_key crypto_user scsi_transport_iscsi ip_gre ip_tunnel gre xt_CONNSECMARK xt_SECMARK xt_state ah6 ah4 nft_objref nft_ct jfs sctp ip6_udp_tunnel udp_tunnel ipmi_watchdog ipmi_poweroff tun xt_multiport xt_nat xt_addrtype xt_mark xt_conntrack nft_chain_nat xt_MASQUERADE nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nft_counter xt_comment nft_compat nf_tables nfnetlink veth bridge stp llc overlay loop dm_log_writes dm_flakey mlx5_ib ib_uverbs ib_core rfkill sunrpc acpi_ipmi ipmi_ssif mlx5_core joydev cdc_ether mlxfw usbnet psample mii tls ipmi_devintf ipmi_msghandler arm_cmn arm_dsu_pmu cppc_cpufreq acpi_tad vfat fat xfs fuse zram ip_tables ast i2c_algo_bit drm_vram_helper drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops cec crct10dif_ce drm_ttm_helper uas ghash_ce ttm sbsa_gwdt nvme drm nvme_core usb_storage xgene_hwmon aes_neon_bs [last unloaded: scsi_debug] 
[ 6183.970142] CPU: 141 PID: 1357992 Comm: fio Tainted: G        W        --------- ---  5.14.0-0.rc6.46.test.fc35.aarch64 #1 
[ 6183.981174] Hardware name: WIWYNN Mt.Jade Server System B81.030Z1.0007/Mt.Jade Motherboard, BIOS 1.6.20210526 (SCP: 1.06.20210526) 2021/05/26 
[ 6183.993854] pstate: 00400009 (nzcv daif +PAN -UAO -TCO BTYPE=--) 
[ 6183.999850] pc : blk_mq_put_rq_ref+0x20/0xb4 
[ 6184.004139] lr : bt_iter+0x64/0xd0 
[ 6184.007530] sp : ffff8000466eb980 
[ 6184.010833] x29: ffff8000466eb980 x28: ffff08004cbfa420 x27: 0000000000400cc0 
[ 6184.017956] x26: ffff3fffb0b48860 x25: 00000000000000c0 x24: 0000000000000010 
[ 6184.025079] x23: 0000000000000000 x22: 0000000000000001 x21: ffff08004cce0000 
[ 6184.032204] x20: ffff8000466eba50 x19: ffff0800523c1880 x18: 0000000000000000 
[ 6184.039328] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 
[ 6184.046450] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000 
[ 6184.053573] x11: 0000000000000000 x10: 0000000000000000 x9 : ffffc6cb43cb5d74 
[ 6184.060697] x8 : ffff8000466ebc00 x7 : ffffffffffffc000 x6 : 000000000000000e 
[ 6184.067820] x5 : 0000000000000000 x4 : 0000000000000001 x3 : ffff0800523c1968 
[ 6184.074944] x2 : 0000000000000000 x1 : ffff0800523c1880 x0 : ffff0800523c1880 
[ 6184.082069] Call trace: 
[ 6184.084504]  blk_mq_put_rq_ref+0x20/0xb4 
[ 6184.088415]  bt_iter+0x64/0xd0 
[ 6184.091459]  blk_mq_queue_tag_busy_iter+0x1a0/0x300 
[ 6184.096328]  blk_mq_in_flight+0x30/0x44 
[ 6184.100152]  part_stat_show+0x60/0x160 
[ 6184.103892]  dev_attr_show+0x2c/0x6c 
[ 6184.107461]  sysfs_kf_seq_show+0x94/0x140 
[ 6184.111463]  kernfs_seq_show+0x38/0x44 
[ 6184.115201]  seq_read_iter+0x1dc/0x4f0 
[ 6184.118949]  kernfs_fop_read_iter+0x44/0x50 
[ 6184.123120]  new_sync_read+0xdc/0x154 
[ 6184.126775]  vfs_read+0x158/0x1e4 
[ 6184.130078]  ksys_read+0x64/0xf0 
[ 6184.133294]  __arm64_sys_read+0x28/0x34 
[ 6184.137118]  invoke_syscall+0x50/0x120 
[ 6184.140882]  el0_svc_common+0x48/0x100 
[ 6184.144619]  do_el0_svc+0x34/0xa0 
[ 6184.147923]  el0_svc+0x2c/0x54 
[ 6184.150984]  el0t_64_sync_handler+0xa4/0x130 
[ 6184.155242]  el0t_64_sync+0x19c/0x1a0 
[ 6184.158897] Code: a9bf7bfd aa0003e1 910003fd f9400802 (f9415c42)  
[ 6184.164983] ---[ end trace 6e354b7ac06e23dd ]--- 

2. What is the Version-Release number of the kernel:
5.14.0-0.rc6.46.test.fc35.aarch64

So far we've hit this only once.

[1] https://gitlab.com/cki-project/kernel-tests/-/tree/main/storage/blktests/blk