17.9.4. schedule
Let’s block the entire kernel! Yay:
./run --eval-after 'dmesg -n 1;insmod schedule.ko schedule=0'
Outcome: the system hangs, the only way out is to kill the VM.
Source: kernel_modules/schedule.c
kthreads only allow interrupting if you call schedule(), and the schedule=0 kernel module parameter turns it off.
Sleep functions like usleep_range also end up calling schedule.
If we allow schedule() to be called, then the system becomes responsive:
./run --eval-after 'dmesg -n 1;insmod schedule.ko schedule=1'
and we can observe the counting with:
dmesg -w
The system also responds if we add another core:
./run --cpus 2 --eval-after 'dmesg -n 1;insmod schedule.ko schedule=0'