I'm getting the following errors in dmesg:

[947174.086041] radeon 0000:01:05.0: alignments 64 1 1 1
[947174.086071] [drm:radeon_cs_ioctl [radeon]] *ERROR* Invalid command stream !
[947185.227119] radeon 0000:01:05.0: texture bo too small ((899 721) (1 1) 0 26
0 -> 2592716 have 4096)
[947185.227132] radeon 0000:01:05.0: alignments 64 1 1 1
[947185.227197] [drm:radeon_cs_ioctl [radeon]] *ERROR* Invalid command stream !
[947197.584009] radeon 0000:01:05.0: texture bo too small ((899 721) (1 1) 0 26
0 -> 2592716 have 4096)
[947197.584016] radeon 0000:01:05.0: alignments 64 1 1 1
[947197.584056] [drm:radeon_cs_ioctl [radeon]] *ERROR* Invalid command stream !
[947243.179560] radeon 0000:01:05.0: texture bo too small ((899 721) (1 1) 0 26
0 -> 2592716 have 4096)
[947243.179567] radeon 0000:01:05.0: alignments 64 1 1 1
[947243.179605] [drm:radeon_cs_ioctl [radeon]] *ERROR* Invalid command stream !

When tooltips are shown in Chromium, their windows contain garbled and
uninitialized pixels. No idea if that is relevant. I'm using Ubuntu 15.10 with
KDE. There were other bugs referencing the "texture bo too small" message, but
they are all very old or marked fixed so I don't think this bug is a dupe.