Comment 3 for bug 1787281

Test on Xenial

Before:

Last login: Wed Aug 15 19:29:38 2018 from 192.168.122.1
$ uname -a
Linux bionic 4.4.0-133-generic #159-Ubuntu SMP Fri Aug 10 07:31:43 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
$ echo 9 | sudo tee /proc/sys/kernel/printk
9
$ sudo losetup --find --show --partscan rlv_grkgld.1mb
<hung>
[ 309.251832] partition (null) (21 pp's found) is not contiguous
[ 309.254557] partition (null) (2 pp's found) is not contiguous
[ 309.256893] partition (null) (1 pp's found) is not contiguous
...
[ 309.335870] partition (null) (2 pp's found) is not contiguous
[ 309.338133] partition (null) (64 pp's found) is not contiguous
[ 309.339719] partition (null) (1 pp's found) is not contiguous
[ 309.345218] BUG: unable to handle kernel paging request at 0000000000001040
[ 309.347776] IP: [<ffffffff8140bb29>] strnlen+0x9/0x40
[ 309.349813] PGD 0
[ 309.350719] Oops: 0000 [#1] SMP
[ 309.351987] Modules linked in: isofs kvm_intel kvm irqbypass input_leds joydev serio_raw sch_fq_codel
ib_iser rdma_cm iw_cm ib_cm ib_sa ib_mad ib_core ib_addr iscsi_tcp libiscsi_tcp libiscsi scsi_transport_i
scsi ip_tables x_tables autofs4 btrfs raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor as
ync_tx xor raid6_pq libcrc32c raid1 raid0 multipath linear psmouse floppy
[ 309.367248] CPU: 1 PID: 979 Comm: losetup Not tainted 4.4.0-133-generic #159-Ubuntu
[ 309.369461] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
[ 309.372403] task: ffff880039a78000 ti: ffff88003b2f0000 task.ti: ffff88003b2f0000
[ 309.375267] RIP: 0010:[<ffffffff8140bb29>] [<ffffffff8140bb29>] strnlen+0x9/0x40
[ 309.377806] RSP: 0018:ffff88003b2f3830 EFLAGS: 00010086
[ 309.379278] RAX: ffffffff81cd2b01 RBX: ffffffff8211eb6c RCX: 0000000000000000
[ 309.381360] RDX: 0000000000001040 RSI: ffffffffffffffff RDI: 0000000000001040
[ 309.384074] RBP: ffff88003b2f3830 R08: 000000000000ffff R09: 000000000000ffff
[ 309.385894] R10: ffff88003b2f39e8 R11: 0000000000000251 R12: 0000000000001040
[ 309.387906] R13: ffffffff8211ef40 R14: 00000000ffffffff R15: 0000000000000000
[ 309.389937] FS: 00007f7e0163c740(0000) GS:ffff88003fc80000(0000) knlGS:0000000000000000
[ 309.392496] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 309.394040] CR2: 0000000000001040 CR3: 0000000039a48000 CR4: 0000000000000670
[ 309.396505] Stack:
[ 309.397306] ffff88003b2f3868 ffffffff8140d8cb ffffffff8211eb6c ffffffff8211ef40
[ 309.400370] ffff88003b2f3980 ffffffff81d00816 ffffffff81d00816 ffff88003b2f38d8
[ 309.403210] ffffffff8140f385 0000000000000092 0000000000000092 000000000000000c
[ 309.406231] Call Trace:
[ 309.407114] [<ffffffff8140d8cb>] string.isra.4+0x3b/0xd0
[ 309.408818] [<ffffffff8140f385>] vsnprintf+0x135/0x530
[ 309.410869] [<ffffffff8140f78d>] vscnprintf+0xd/0x30
[ 309.412283] [<ffffffff810dd5e3>] vprintk_emit+0x123/0x520
[ 309.413983] [<ffffffff810ddb69>] vprintk_default+0x29/0x40
[ 309.415495] [<ffffffff811933c0>] printk+0x5a/0x76
[ 309.417463] [<ffffffff813e9571>] aix_partition+0x5d1/0x600
[ 309.419595] [<ffffffff811956ad>] ? pagecache_get_page+0x2d/0x1c0
[ 309.421218] [<ffffffff813ecefb>] msdos_partition+0x86b/0x880
[ 309.423173] [<ffffffff81252ef0>] ? blkdev_readpages+0x20/0x20
[ 309.424963] [<ffffffff81195a39>] ? read_cache_page+0x19/0x20
[ 309.426515] [<ffffffff813e6ced>] ? read_dev_sector+0x2d/0x90
[ 309.428280] [<ffffffff8140f819>] ? snprintf+0x49/0x60
[ 309.429707] [<ffffffff813ec690>] ? parse_solaris_x86+0x210/0x210
[ 309.432081] [<ffffffff813e80d0>] check_partition+0x140/0x220
[ 309.433845] [<ffffffff813e75cb>] rescan_partitions+0xbb/0x2b0
[ 309.435421] [<ffffffff8135118e>] ? security_capable+0x4e/0x70
[ 309.437006] [<ffffffff813e2545>] __blkdev_reread_part+0x65/0x70
[ 309.438598] [<ffffffff813e2573>] blkdev_reread_part+0x23/0x40
[ 309.440173] [<ffffffff81591a98>] loop_reread_partitions+0x28/0x50
[ 309.442811] [<ffffffff81591e5a>] loop_set_status+0x39a/0x3d0
[ 309.444381] [<ffffffff81592150>] loop_set_status64+0x50/0x70
[ 309.446146] [<ffffffff815934d1>] lo_ioctl+0xf1/0x8b0
[ 309.447547] [<ffffffff813e2dde>] blkdev_ioctl+0x25e/0x910
[ 309.449056] [<ffffffff81235663>] ? __fd_install+0x33/0xe0
[ 309.451395] [<ffffffff81253a7d>] block_ioctl+0x3d/0x50
[ 309.453275] [<ffffffff8122aaff>] do_vfs_ioctl+0x2af/0x4b0
[ 309.455019] [<ffffffff812267e4>] ? putname+0x54/0x60
[ 309.456434] [<ffffffff81215d0f>] ? do_sys_open+0x1bf/0x2a0
[ 309.457943] [<ffffffff8122ad79>] SyS_ioctl+0x79/0x90
[ 309.459886] [<ffffffff8185424e>] entry_SYSCALL_64_fastpath+0x22/0xc1
[ 309.462722] Code: 00 00 80 3f 00 55 48 89 e5 74 11 48 89 f8 48 83 c0 01 80 38 00 75 f7 48 29 f8 5d c3
31 c0 5d c3 66 90 55 48 85 f6 48 89 e5 74 2e <80> 3f 00 74 29 48 8d 57 01 48 8d 04 37 eb 0d 48 8d 4a 01 8
0 79
[ 309.475971] RIP [<ffffffff8140bb29>] strnlen+0x9/0x40
[ 309.477537] RSP <ffff88003b2f3830>
[ 309.478624] CR2: 0000000000001040
[ 309.479703] ---[ end trace 4fe99281b613609c ]---

After:

$ uname -a
Linux bionic 4.4.0-133-generic #159+sf181954.1 SMP Wed Aug 15 14:18:05 -03 2018 x86_64 x86_64 x86_64 GNU/Linux
$ echo 9 | sudo tee /proc/sys/kernel/printk
9
$ sudo losetup --find --show --partscan rlv_grkgld.1mb
/dev/loop0