It's a hung task panic.

<0>[ 1440.319380] Kernel panic - not syncing: hung_task: blocked tasks
<4>[ 1440.319394] CPU: 0 PID: 31 Comm: khungtaskd Tainted: G        W      3.18.0-12867-gba1c24c #1
<4>[ 1440.319405] Hardware name: Mediatek Elm rev2, rev1 board (DT)

The only stack trace that looks interesting is this one:

0>[ 1440.319495] Call trace:
<4>[ 1440.319504] [<ffffffc000209080>] dump_backtrace+0x0/0x160
<4>[ 1440.319510] [<ffffffc0002091fc>] show_stack+0x1c/0x28
<4>[ 1440.319515] [<ffffffc0009016cc>] dump_stack+0x80/0xc4
<4>[ 1440.319521] [<ffffffc0002126f8>] handle_IPI+0x154/0x268
<4>[ 1440.319526] [<ffffffc0002004f8>] gic_handle_irq+0x70/0x88
<4>[ 1440.319530] Exception stack(0xffffffc0fa6af910 to 0xffffffc0fa6afa30)
<4>[ 1440.319536] f900:                                     01102478 ffffffc0 00000000 00000000
<4>[ 1440.319541] f920: fa6afa50 ffffffc0 00270c34 ffffffc0 fa695300 ffffffc0 dc8cb000 cb88537f
<4>[ 1440.319547] f940: dc8cb000 cb88537f 00000000 00000000 00000001 00000000 00000000 00000000
<4>[ 1440.319553] f960: 00000000 00000000 00325144 ffffffc0 00009800 00000000 010fcef0 ffffffc0
<4>[ 1440.319558] f980: 00000004 00000000 00000020 00000000 3a797469 6e6f6e20 66202c65 75716572
<4>[ 1440.319564] f9a0: 79636e65 3235203a 8172fff3 ffffffc0 8172ffe3 ffffffc0 00000000 00000000
<4>[ 1440.319569] f9c0: 00000000 00000000 01102478 ffffffc0 00000000 00000000 a5dae718 ffffffc0
<4>[ 1440.319574] f9e0: 00000000 00000000 00000000 00000000 00000000 00000000 00000001 00000000
<4>[ 1440.319579] fa00: 00000000 00000000 00325144 ffffffc0 00000140 00000000 fa6afa60 ffffffc0
<4>[ 1440.319584] fa20: 00270c20 ffffffc0 fa6afa50 ffffffc0
<4>[ 1440.319589] [<ffffffc000203da8>] el1_irq+0x68/0xe0
<4>[ 1440.319594] [<ffffffc000907c64>] _raw_spin_lock+0x4c/0x64
<4>[ 1440.319601] [<ffffffc000325140>] list_lru_count_node+0x30/0x80
<4>[ 1440.319607] [<ffffffc000352334>] super_cache_count+0x5c/0x98
<4>[ 1440.319613] [<ffffffc000312a50>] shrink_slab_node+0x5c/0x3a8
<4>[ 1440.319617] [<ffffffc000313600>] shrink_slab+0x88/0x120
<4>[ 1440.319622] [<ffffffc00031627c>] balance_pgdat+0x304/0x4e4
<4>[ 1440.319627] [<ffffffc000316900>] kswapd+0x4a4/0x568
<4>[ 1440.319632] [<ffffffc000242ee0>] kthread+0xf0/0xfc

The other CPUs aren't doing anything interesting.

Was the chromebook swapping heavily at this time?  It seems unlikely because from your description you weren't doing anything with it, correct?  But then why was kswapd running at all?

I wasn't doing anything with it, it was idle while running the task manager in the background.

I remember from one of our discussions earlier that reading totmaps (which is done by the task manager) traverses pages, correct? Does that cause kswapd to run often?

This bug has an owner, thus, it's been triaged. Changing status to "assigned".