[AT&T Samsung Galaxy S II SGH-I777] cyril279:
The device rebooted on its own while in TWRP? This concerns me because the device should remain in TWRP until prompted to reboot.

EDIT: yeah, something's still not right, I installed the shift4.7-twrp kernel, rebooted to recovery, and let it sit. The device rebooted on its own within five minutes (10:26 reboot into TWRP - 10:30 spontaneous reboot)

A complete /data backup is still possible because some /data partitions are small enough for the process to complete before the reboot.

The corrupt backups are a result of the device spontaneously rebooting DURING a backup (doesn't matter which partition)

<6>[ 230.460526] c0 max17042_need_soc_recal: HW(0xe)
<6>[ 230.460691] c0 max17042 9-0036: max17042_get_soc : use raw (81), soc (83)
<6>[ 233.285940] c0 sec-battery sec-battery: sec_bat_check_vf: Battery Health (1)
<3>[ 240.190266] c0 [B][COLOR="Red"]INFO: task kinteractiveup:1063 blocked for more than 120 seconds.[/COLOR][/B]
<3>[ 240.196671] c0 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
<6>[ 240.204728] c0 kinteractiveup D c0f7e8c4 0 1063 2 0x00000000
<4>[ 240.204969] c0 Backtrace:
<4>[ 240.205296] c0 [<c0f7e55c>] (__schedule+0x0/0x804) from [<c0f7eeb0>] (schedule+0x50/0x68)
<4>[ 240.205587] c0 [<c0f7ee60>] (schedule+0x0/0x68) from [<c0a6d444>] (kthread+0x70/0x94)
<4>[ 240.206091] c0 [<c0a6d3d4>] (kthread+0x0/0x94) from [<c0a5570c>] (do_exit+0x0/0x698)
<4>[ 240.206301] c0 r6:c0a5570c r5:c0a6d3d4 r4:e4043f04
<0>[ 240.206516] c0 [B][COLOR="red"]Kernel panic - not syncing: hung_task: blocked tasks[/COLOR][/B]
<6>[ 240.212012] c0 notifier_call_chain : NOTIFY BAD sec_debug_panic_handler
<0>[ 240.218200] c0 Rebooting in 1 seconds..
<0>[ 241.233783] c0 sec_reboot (104, (null))
Ibl: pbl_read_emmc441() read 8k
Ibl: pbl_read_emmc441() read 96k
Ibl: pbl_read_emmc441() read download info
Ibl: pbl_read_emmc441() endop
Ibl: jump() verify_binary_integrity...ok
Ibl: jump() jump!!!

If you push your changes to github I can review further.

---------- Post added at 11:13 AM ---------- Previous post was at 10:15 AM ----------

My recommendation: Put interactive to sleep as well.

Your current defconfig (from line 755):

CONFIG_CPU_FREQ_GOV_ONDEMAND_FLEXRATE=y
CONFIG_CPU_FREQ_GOV_ONDEMAND_FLEXRATE_MAX_DURATION=100
CONFIG_CPU_FREQ_GOV_INTERACTIVE=y
CONFIG_CPU_FREQ_GOV_CONSERVATIVE=y
CONFIG_CPU_FREQ_GOV_ADAPTIVE=y
CONFIG_CPU_FREQ_GOV_PEGASUSQ=y

Omni known good defconfig (from matching code line):

CONFIG_CPU_FREQ_GOV_ONDEMAND_FLEXRATE=y
CONFIG_CPU_FREQ_GOV_ONDEMAND_FLEXRATE_MAX_DURATION=100
# CONFIG_CPU_FREQ_GOV_INTERACTIVE is not set
CONFIG_CPU_FREQ_GOV_CONSERVATIVE=y
# CONFIG_CPU_FREQ_GOV_ADAPTIVE is not set
CONFIG_CPU_FREQ_GOV_PEGASUSQ=y

log that provided that got ADAPTIVE put back to sleep on Omni:

<3>[ 240.160335] c0 [B][COLOR="Red"]INFO: task kadaptiveup:1044 blocked for more than 120 seconds[/COLOR][/B].
<3>[ 240.160463] c0 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
<6>[ 240.160606] c0 kadaptiveup D c0bf5d4c 0 1044 2 0x00000000
<4>[ 240.160750] c0 Backtrace:
<4>[ 240.160894] c0 [<c0bf59d4>] (__schedule+0x0/0x840) from [<c0bf6370>] (schedule+0x50/0x68)
<4>[ 240.161076] c0 [<c0bf6320>] (schedule+0x0/0x68) from [<c06f596c>] (kthread+0x70/0x94)
<4>[ 240.161244] c0 [<c06f58fc>] (kthread+0x0/0x94) from [<c06dd8b4>] (do_exit+0x0/0x6cc)
<4>[ 240.161379] c0 r6:c06dd8b4 r5:c06f58fc r4:e4043f04
<0>[ 240.161509] c0 Kernel panic - not syncing: hung_task: blocked tasks
<4>[ 240.161617] c0 Backtrace:
<4>[ 240.161730] c0 [<c06a3588>] (dump_backtrace+0x0/0x10c) from [<c0bf0908>] (dump_stack+0x18/0x1c)
<4>[ 240.161877] c0 r6:e43075a8 r5:c0f34740 r4:c0fbe7e0 r3:00000000
<4>[ 240.162055] c0 [<c0bf08f0>] (dump_stack+0x0/0x1c) from [<c0bf0ca0>] (panic+0x80/0x1ac)
<4>[ 240.162235] c0 [<c0bf0c20>] (panic+0x0/0x1ac) from [<c071ef90>] (watchdog+0x270/0x29c)
<4>[ 240.162370] c0 r3:00000001 r2:c0f15b70 r1:00000000 r0:c0d1ed90
<4>[ 240.162516] c0 r7:000003da
<4>[ 240.162616] c0 [<c071ed20>] (watchdog+0x0/0x29c) from [<c06f5988>] (kthread+0x8c/0x94)
<4>[ 240.162777] c0 [<c06f58fc>] (kthread+0x0/0x94) from [<c06dd8b4>] (do_exit+0x0/0x6cc)
<4>[ 240.162910] c0 r6:c06dd8b4 r5:c06f58fc r4:e4043f24
<6>[ 240.163216] c0 notifier_call_chain : NOTIFY BAD sec_debug_panic_handler
<0>[ 240.163344] c0 Rebooting in 1 seconds..
<0>[ 241.167473] c0 sec_reboot (104, (null))
Ibl: pbl_read_emmc441() read 8k
Ibl: pbl_read_emmc441() read 96k
Ibl: pbl_read_emmc441() read download info
Ibl: pbl_read_emmc441() endop
Ibl: jump() verify_binary_integrity...ok
Ibl: jump() jump!!!