I can reproduce the bug on a fresh installation of Disco/armhf rpi3.
Moreover, the bug appears to be kernel in-kernel - by installing the Disco kernel on a Bionic image (that didn't show any abnormal load with its Bionic/armhf kernel), the bug appears there too.
The bug is reproducible as early as Ubuntu-raspi2-5.0.0-1002.2, and before that there's the Broadcom BSP, and the initial config sync wrt bcm2709_defconfig - bisecting the Broadcom BSP is a bit problematic, because removing patches, often, breaks the build.
I can reproduce the bug on a fresh installation of Disco/armhf rpi3.
Moreover, the bug appears to be kernel in-kernel - by installing the Disco kernel on a Bionic image (that didn't show any abnormal load with its Bionic/armhf kernel), the bug appears there too.
The bug is reproducible as early as Ubuntu- raspi2- 5.0.0-1002. 2, and before that there's the Broadcom BSP, and the initial config sync wrt bcm2709_defconfig - bisecting the Broadcom BSP is a bit problematic, because removing patches, often, breaks the build.