Comment 44 for bug 1867916

Xenial / Testing
======

modified
--------

$ uname -rv
4.4.0-186-generic #216+lp1867916.1 SMP Mon Jul 6 18:45:47 -03 2020

$ sudo make-bcache --bdev $DEV --block 8k
[ 60.860259] bcache: bcache_device_init() bcache0: sb/logical block size (8192) greater than page size (4096) falling back to device logical block size (512)
[ 60.860312] bcache: register_bdev() registered backing device loop0

original
--------

$ uname -rv
4.4.0-186-generic #216-Ubuntu SMP Wed Jul 1 05:34:05 UTC 2020

$ sudo make-bcache --bdev $DEV --block 8k
[ 22.192801] bcache: register_bdev() registered backing device loop0
[ 22.197141] BUG: unable to handle kernel NULL pointer dereference at 0000000000000098
[ 22.198983] IP: [<ffffffff8125acb0>] bdev_read_page+0x10/0xb0
[ 22.200283] PGD 0
[ 22.200843] Oops: 0000 [#1] SMP
[ 22.201796] Modules linked in: bcache isofs kvm_intel input_leds kvm irqbypass joydev serio_raw ib_iser rdma_cm iw_cm ib_cm ib_sa ib_mad
ib_core ib_addr iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi autofs4 btrfs xor raid6_pq psmouse floppy
[ 22.208162] CPU: 1 PID: 1301 Comm: systemd-udevd Not tainted 4.4.0-186-generic #216-Ubuntu
[ 22.209642] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
[ 22.211045] task: ffff8800b97ea700 ti: ffff8800b9b78000 task.ti: ffff8800b9b78000
[ 22.212244] RIP: 0010:[<ffffffff8125acb0>] [<ffffffff8125acb0>] bdev_read_page+0x10/0xb0
[ 22.213616] RSP: 0018:ffff8800b9b7ba80 EFLAGS: 00010283
[ 22.214513] RAX: 0000000000000004 RBX: 0000000000000000 RCX: 0000000000000004
[ 22.215730] RDX: ffffea0004e55280 RSI: fff8800b9b7bb580 RDI: 0000000000000000
[ 22.217220] RBP: ffff8800b9b7baa0 R08: ffff8800b9b7bbb8 R09: ffff8800b9b7bbb0
[ 22.218640] R10: ffff8800368b4df8 R11: fff8800b9b7bb580 R12: 0000000000000000
[ 22.220114] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[ 22.221574] FS: 00007f5df7bd28c0(0000) GS:ffff88013fc80000(0000) knlGS:0000000000000000
[ 22.223416] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 22.224584] CR2: 0000000000000098 CR3: 00000000b9b76000 CR4: 0000000000000670
[ 22.225945] Stack:
[ 22.226534] 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 22.228516] ffff8800b9b7bb78 ffffffff81261bbe ffff8800368b4f80 ffff8800b9b7bba8
[ 22.230532] 0000000000000000 ffff8800b9b7bbb8 ffff8800b9b7bbb0 ffffffff8125a6b0
[ 22.232485] Call Trace:
[ 22.233148] [<ffffffff81261bbe>] do_mpage_readpage+0x52e/0x7a0
[ 22.234384] [<ffffffff8125a6b0>] ? I_BDEV+0x20/0x20
[ 22.235487] [<ffffffff811abebe>] ? lru_cache_add+0xe/0x10
[ 22.236675] [<ffffffff81261f42>] mpage_readpages+0x112/0x190
[ 22.237903] [<ffffffff8125a6b0>] ? I_BDEV+0x20/0x20
[ 22.238960] [<ffffffff8125a6b0>] ? I_BDEV+0x20/0x20
[ 22.240025] [<ffffffff811f09dc>] ? alloc_pages_current+0x8c/0x110
[ 22.241308] [<ffffffff8125b1cd>] blkdev_readpages+0x1d/0x20
[ 22.242463] [<ffffffff811a9f39>] __do_page_cache_readahead+0x199/0x240
[ 22.243843] [<ffffffff811aa34a>] force_page_cache_readahead+0xaa/0x100
[ 22.245267] [<ffffffff811aa3df>] page_cache_sync_readahead+0x3f/0x50
[ 22.246572] [<ffffffff8119d0ba>] generic_file_read_iter+0x54a/0x6b0
[ 22.247876] [<ffffffff8125bcc5>] blkdev_read_iter+0x35/0x40
[ 22.249132] [<ffffffff8121e14e>] new_sync_read+0x9e/0xe0
[ 22.250312] [<ffffffff8121e1b9>] __vfs_read+0x29/0x40
[ 22.251460] [<ffffffff8121e926>] vfs_read+0x86/0x130
[ 22.252590] [<ffffffff8121f67c>] SyS_read+0x5c/0xe0
[ 22.253672] [<ffffffff8186991b>] entry_SYSCALL_64_fastpath+0x22/0xd0
[ 22.255015] Code: 83 f8 a1 0f 45 d8 89 d8 5b 41 5c 5d c3 0f 1f 40 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 48 89 e5 41 56 41 55
 41 54 53 <48> 8b 87 98 00 00 00 4c 8b b0 c0 03 00 00 49 83 7e 10 00 74 7c
[ 22.264489] RIP [<ffffffff8125acb0>] bdev_read_page+0x10/0xb0
[ 22.265778] RSP <ffff8800b9b7ba80>
[ 22.266602] CR2: 0000000000000098
[ 22.267432] ---[ end trace ae0520addf7365b3 ]---