Comment 46 for bug 1867916

Disco / Testing
=====

* Using the linux-hwe-5.0 from "Disco" (EOL) on Bionic for the 5.0 kernel.

modified
--------

$ uname -rv
5.0.0-57-generic #61~18.04.1+lp1867916.1 SMP Mon Jul 6 19:27:05 -03 2020

$ sudo make-bcache --bdev $DEV --block 8k
[ 109.818171] bcache: bcache_device_init() bcache0: sb/logical block size (8192) greater than page size (4096) falling back to device logical block size (512)
[ 109.822055] bcache: register_bdev() registered backing device loop0

original
--------

$ uname -rv
5.0.0-57-generic #61~18.04.1-Ubuntu SMP Mon Jul 6 09:40:52 UTC 2020

$ sudo make-bcache --bdev $DEV --block 8k
[ 112.148300] bcache: register_bdev() registered backing device loop0
[ 112.150575] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
[ 112.153000] #PF error: [normal kernel read fault]
[ 112.154474] PGD 800000012a5df067 P4D 800000012a5df067 PUD 137558067 PMD 0
[ 112.156614] Oops: 0000 [#1] SMP PTI
[ 112.157742] CPU: 1 PID: 1649 Comm: bcache-register Not tainted 5.0.0-57-generic #61~18.04.1-Ubuntu
[ 112.161386] RIP: 0010:create_empty_buffers+0x29/0x110
[ 112.162321] Code: 00 0f 1f 44 00 00 55 48 89 e5 41 55 41 54 53 49 89 d5 ba 01 00 00 00 48 89 fb e8 72 fe ff ff 49 89 c4 48 89 c2 eb 03 4$ 89 ca <48> 8b 4a 08 4c 09 2a 48 85 c9 75 f1 4c 89 62 08 48 8b 43 18 48 8d
[ 112.165333] RSP: 0018:ffff9fac40dd77f8 EFLAGS: 00010286
[ 112.166198] RAX: 0000000000000000 RBX: ffffc8b744a73700 RCX: ffff9051b779d000
[ 112.167430] RDX: 0000000000000000 RSI: ffff9051b779d000 RDI: ffffc8b744a73700
[ 112.168767] RBP: ffff9fac40dd7810 R08: dead0000000000ff R09: 0000000000000003
[ 112.169992] R10: 0000000000000000 R11: 00003748bb58c8ff R12: 0000000000000000
[ 112.171515] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000200
[ 112.172649] FS: 00007f4344d58700(0000) GS:ffff9051bba80000(0000) knlGS:0000000000000000
[ 112.174052] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 112.175056] CR2: 0000000000000008 CR3: 0000000129e2a000 CR4: 00000000000006e0
[ 112.176259] Call Trace:
[ 112.176773] create_page_buffers+0x52/0x60
[ 112.177525] block_read_full_page+0x4e/0x3c0
[ 112.178304] ? check_disk_change+0x70/0x70
[ 112.179098] ? count_shadow_nodes+0x130/0x130
[ 112.179881] blkdev_readpage+0x18/0x20
[ 112.180571] do_read_cache_page+0x37b/0x790
[ 112.181324] ? blkdev_writepages+0x10/0x10
[ 112.182064] ? get_page_from_freelist+0x154e/0x1560
[ 112.182924] ? update_load_avg+0x8b/0x5f0
[ 112.183657] read_cache_page+0x12/0x20
[ 112.184354] read_dev_sector+0x2d/0xe0
[ 112.185041] read_lba+0x130/0x220
[ 112.185665] efi_partition+0x131/0x770
[ 112.186360] ? string+0x60/0x90
[ 112.186971] ? vsnprintf+0xfb/0x510
[ 112.187625] ? snprintf+0x45/0x70
[ 112.188252] ? is_gpt_valid.part.7+0x420/0x420
[ 112.189056] check_partition+0x13f/0x250
[ 112.189759] ? is_gpt_valid.part.7+0x420/0x420
[ 112.190542] ? check_partition+0x13f/0x250
[ 112.191292] rescan_partitions+0xaf/0x360
[ 112.192015] bdev_disk_changed+0x5a/0x60
[ 112.192723] __blkdev_get+0x354/0x560
[ 112.193440] ? inode_init_always+0x131/0x1f0
[ 112.194365] blkdev_get+0x131/0x340
[ 112.195106] ? wake_up_bit+0x42/0x50
[ 112.195867] ? unlock_new_inode+0x4f/0x80
[ 112.196744] ? bdget+0x109/0x120
[ 112.197436] __device_add_disk+0x3d6/0x4f0
[ 112.198315] device_add_disk+0x13/0x20
[ 112.199132] bch_cached_dev_run.part.32+0x44/0x1b0 [bcache]
[ 112.200248] register_bcache+0xa28/0x1120 [bcache]
[ 112.201214] kobj_attr_store+0x12/0x20
[ 112.201977] ? kobj_attr_store+0x12/0x20
[ 112.202802] sysfs_kf_write+0x3c/0x50
[ 112.203584] kernfs_fop_write+0x13e/0x1c0
[ 112.204458] __vfs_write+0x1b/0x40
[ 112.205164] vfs_write+0xb1/0x1a0
[ 112.205860] ksys_write+0x5c/0xe0
[ 112.206578] __x64_sys_write+0x1a/0x20
[ 112.207388] do_syscall_64+0x5a/0x120
[ 112.208157] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 112.209206] RIP: 0033:0x7f43448682c0
[ 112.209956] Code: 73 01 c3 48 8b 0d d8 cb 2c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d 89 24 2d 00 00 75 10 b8 01 00 00 00
 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 fe dd 01 00 48 89 04 24
[ 112.213375] RSP: 002b:00007ffe6225fcf8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[ 112.214816] RAX: ffffffffffffffda RBX: 000000000000000b RCX: 00007f43448682c0
[ 112.216142] RDX: 000000000000000b RSI: 0000000000dc9010 RDI: 0000000000000003
[ 112.217477] RBP: 0000000000dc9010 R08: 0000000000000000 R09: 000000000000000b
[ 112.218831] R10: 000000000000000a R11: 0000000000000246 R12: 000000000000000b
[ 112.220143] R13: 0000000000000001 R14: 00007ffe6225fd70 R15: 0000000000000000
[ 112.221450] Modules linked in: bcache crc64 isofs kvm_intel kvm irqbypass input_leds joydev serio_raw ib_iser rdma_cm iw_cm ib_cm ib_core
 iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi autofs4 btrfs zstd_compress raid10 raid456 async_raid6_recov async_memcpy async_pq asy
nc_xor async_tx xor raid6_pq libcrc32c raid1 raid0 multipath linear psmouse virtio_net net_failover virtio_blk failover floppy
[ 112.227818] CR2: 0000000000000008
[ 112.228591] ---[ end trace c425c5c71d7443c3 ]---
[ 112.229535] RIP: 0010:create_empty_buffers+0x29/0x110
[ 112.230501] Code: 00 0f 1f 44 00 00 55 48 89 e5 41 55 41 54 53 49 89 d5 ba 01 00 00 00 48 89 fb e8 72 fe ff ff 49 89 c4 48 89 c2 eb 03 48
 89 ca <48> 8b 4a 08 4c 09 2a 48 85 c9 75 f1 4c 89 62 08 48 8b 43 18 48 8d
[ 112.233933] RSP: 0018:ffff9fac40dd77f8 EFLAGS: 00010286
[ 112.234912] RAX: 0000000000000000 RBX: ffffc8b744a73700 RCX: ffff9051b779d000
[ 112.236245] RDX: 0000000000000000 RSI: ffff9051b779d000 RDI: ffffc8b744a73700
[ 112.237589] RBP: ffff9fac40dd7810 R08: dead0000000000ff R09: 0000000000000003
[ 112.239009] R10: 0000000000000000 R11: 00003748bb58c8ff R12: 0000000000000000
[ 112.240337] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000200
[ 112.241646] FS: 00007f4344d58700(0000) GS:ffff9051bba80000(0000) knlGS:0000000000000000
[ 112.243230] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 112.244303] CR2: 0000000000000008 CR3: 0000000129e2a000 CR4: 00000000000006e0