A few times in a month, my computer fails to resume and just hangs, with black
screen, and needs hard reset. This time I got lucky and kernel panic text was
shown on my screen, so I took a shot of it. There's a lot of [ttm] and [radeon]
strings in it, so it looks like it is related to my Radeon card. The text on
the screen has "scrolled" once in a while (it seemed to be rotation), I hope I
captured everything important.

Components:
Radeon R9 270:
01:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc.
[AMD/ATI] Curacao PRO [Radeon R7 370 / R9 270/370 OEM] [1002:6811]
fully updated Fedora 22:
kernel-4.0.7-300.fc22.x86_64
xorg-x11-server-Xorg-1.17.2-1.fc22.x86_64
xorg-x11-drv-ati-7.5.0-3.fc22.x86_64
libdrm-2.4.61-3.fc22.x86_64
mesa-dri-drivers-10.6.1-1.20150629.fc22.x86_64


Please tell me if I can add more useful information somehow. That issue is not
easily reproducible, it happens rarely and usually I just see a black screen,
so I can't even tell whether it is always the same issue or not.