Comment 2 for bug 1431196

Example of bad thing:

[ 95.307704] Oops: Exception in kernel mode, sig: 4 [#1]
[ 95.307869] SMP NR_CPUS=2048 NUMA PowerNV
[ 95.307923] Modules linked in: i2c_dev bnep rfcomm bluetooth 6lowpan_iphc joydev mac_hid ast ttm hid_generic drm_kms_helper usbhid drm hid syscopyarea at24 sysfillrect sysimgblt i2c_algo_bit uio_pdrv_genirq uio rtc_generic i2c_opal powernv_rng parport_pc ppdev lp parport mlx4_en vxlan uas usb_storage mlx4_core ahci libahci
[ 95.308294] CPU: 1 PID: 3017 Comm: test-i2c Not tainted 3.16.0-32-generic #42
[ 95.308346] task: c00000077fd35200 ti: c00000077fdbc000 task.ti: c00000077fdbc000
[ 95.308399] NIP: c0000007fe0b7c44 LR: 0000000000000000 CTR: c00000000006e86f
[ 95.308451] REGS: c00000077fdbf7a0 TRAP: 0e40 Not tainted (3.16.0-32-generic)
[ 95.308502] MSR: 9000000000081002 <SF,HV,ME,RI> CR: 28000022 XER: 00000000
[ 95.308599] CFAR: d00000000fcd08bc SOFTE: 1
GPR00: 000000000000006d c00000077fdbfa20 c0000007fe0c4948 0000000000000000
GPR04: 0000000000000001 c00000077fdbfb10 0000000000000000 0000000000000000
GPR08: 0000000000000000 0000000000000000 0000000000000000 c0000007fe0b7c38
GPR12: c0000007fe0b7c40 c00000000fb80900 0000000000000000 0000000000000000
GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
GPR24: 0000000000000000 00000000ffff3819 0000000000000002 c000000784a20690
GPR28: c000000001422180 0000000000000001 0000000000000000 c00000077fdbfb10
[ 95.309272] NIP [c0000007fe0b7c44] 0xc0000007fe0b7c44
[ 95.309308] LR [0000000000000000] (null)
[ 95.309342] Call Trace:
[ 95.309364] [c00000077fdbfa20] [d00000000fcd00e0] i2c_opal_send_request+0x50/0x120 [i2c_opal] (unreliable)
[ 95.309435] [c00000077fdbfaf0] [d00000000fcd0500] i2c_opal_master_xfer+0xd0/0x1d0 [i2c_opal]
[ 95.309498] [c00000077fdbfb50] [c0000000007efd44] __i2c_transfer+0xb4/0x350
[ 95.309551] [c00000077fdbfbb0] [c0000000007f3b28] i2c_transfer+0xc8/0x160
[ 95.309604] [c00000077fdbfc30] [d0000000151906b0] i2cdev_ioctl_rdrw+0x180/0x340 [i2c_dev]
[ 95.309665] [c00000077fdbfcb0] [d000000015190dcc] i2cdev_ioctl+0x24c/0x370 [i2c_dev]
[ 95.309732] [c00000077fdbfd40] [c0000000002c9940] do_vfs_ioctl+0x470/0x780
[ 95.309786] [c00000077fdbfde0] [c0000000002c9d24] SyS_ioctl+0xd4/0xf0
[ 95.309839] [c00000077fdbfe30] [c00000000000a17c] syscall_exit+0x0/0x7c