Comment 0 for bug 1980951

---Problem Description from Peter---
A kernel oops occurs when a device is removed from the cio_ignore list on a system with non-I/O subchannels (e.g. SCM or CHSC subchannels). As a result, previously ignored devices cannot be activated, and new devices cannot be found.

---uname output---
Linux localhost 5.15.0-40-generic #43-Ubuntu SMP Wed Jun 15 12:53:53 UTC 2022 s390x s390x s390x GNU/Linux

Machine Type = s390x

---Steps to Reproduce---
On an s390x-LPAR with non-I/O subchannels, remove a device from the cio_ignore list.

Oops output:
 [ 51.597505] Unable to handle kernel pointer dereference in virtual kernel address space
[ 51.597516] Failing address: 2081e99191e98000 TEID: 2081e99191e98803
[ 51.597520] Fault in home space mode while using kernel ASCE.
[ 51.597524] AS:0000000082adc007 R3:0000000000000024
[ 51.597665] Oops: 0038 ilc:3 [#1] SMP
[ 51.597671] Modules linked in: scm_block chsc_sch vfio_ccw mdev vfio_iommu_type1 vfio eadm_sch sch_fq_codel dm_multipath scsi_dh_rdac scsi_dh_emc scsi_dh_alua drm i2c_core drm_panel_orientation_quirks ip_tables x_tables btrfs blake2b_generic zstd_compress raid10 raid456 async_raid6_recov async_memcpy async_pq async_
xor async_tx xor raid6_pq libcrc32c raid1 raid0 linear pkey zcrypt crc32_vx_s390 ghash_s390 prng chacha_s390 libchacha aes_s390 des_s390 libdes qeth_l2 bridge stp llc zfcp qeth qdio scsi_transport_fc ccwgroup sha512_s390 sha256_s390 sha1_s390 sha_common
[ 51.597735] CPU: 6 PID: 1418 Comm: cio_ignore Not tainted 5.15.0-40-generic #43-Ubuntu
[ 51.597740] Hardware name: IBM 2964 NC9 702 (LPAR)
[ 51.597742] Krnl PSW : 0704e00180000000 0000000081b0c632 (__unset_online+0x22/0x70)
[ 51.597752] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3
[ 51.597756] Krnl GPRS: 0000000000000001 00000000004a3ca8 0000038007e49000 2081e99191e98528
[ 51.597760] 0000000000000000 0000000081b0c610 0000000000000000 0000000081b07f10
[ 51.597762] 000002aa00000000 0000000081b0c610 0000038007e49000 0000038007a6bc98
[ 51.597765] 00000000941f9200 000003ffa8cf95e0 0000000081818900 0000038007a6bbf8
[ 51.597773] Krnl Code: 0000000081b0c624: a784000c brc 8,0000000081b0c63c
[ 51.597773] 0000000081b0c628: e33030200002 ltg %r3,32(%r3)
[ 51.597773] #0000000081b0c62e: a7840007 brc 8,0000000081b0c63c
[ 51.597773] >0000000081b0c632: e33032000012 lt %r3,512(%r3)
[ 51.597773] 0000000081b0c638: a7740007 brc 7,0000000081b0c646
[ 51.597773] 0000000081b0c63c: a7290000 lghi %r2,0
[ 51.597773] 0000000081b0c640: c0f400089854 brcl 15,0000000081c1f6e8
[ 51.597773] 0000000081b0c646: ebeff0880024 stmg %r14,%r15,136(%r15)
[ 51.597818] Call Trace:
[ 51.597820] [<0000000081b0c632>] __unset_online+0x22/0x70
[ 51.597824] ([<00000000818188e6>] bus_for_each_dev+0x66/0xc0)
[ 51.597828] [<0000000081b0e378>] css_schedule_eval_cond+0xe8/0x130
[ 51.597832] [<0000000081b08062>] cio_ignore_write+0x152/0x190
[ 51.597838] [<00000000814be36e>] proc_reg_write+0x9e/0xf0
[ 51.597843] [<00000000813f3470>] vfs_write+0xc0/0x280
[ 51.597848] [<00000000813f59a8>] ksys_write+0x68/0x100
[ 51.597852] [<0000000081b495d0>] __do_syscall+0x1c0/0x1f0
[ 51.597857] [<0000000081b56858>] system_call+0x78/0xa0
[ 51.597862] Last Breaking-Event-Address:
[ 51.597864] [<000000000000a000>] 0xa000
[ 51.597868] ---[ end trace 166ba86e913d2c60 ]---