Re: [PATCH] KVM: Move VM's worker kthreads back to the original cgroups before exiting.

On Tue, Dec 14, 2021 at 4:13 PM Vipin Sharma [off-list ref] wrote:

VM worker kthreads can linger in the VM process's cgroup for sometime
after KVM temrinates the VM process.

KVM terminates the worker kthreads by calling kthread_stop() which waits
on the signal generated by exit_mm() in do_exit() during kthread's exit.
However, these kthreads are removed from the cgroup using cgroup_exit()
call which happens after exit_mm() in do_exit(). A VM process can
terminate between the time window of exit_mm() to cgroup_exit(), leaving
only worker kthreads in the cgroup.

Moving worker kthreads back to the original cgroup (kthreadd_task's
cgroup) makes sure that cgroup is empty as soon as the main VM process
is terminated.

Signed-off-by: Vipin Sharma <redacted>
---
 virt/kvm/kvm_main.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

Hello

Off-topic, can this kvm worker_thread and the thread to do async pagefault
be possibly changed to use something like io_uring's IOWQ (fs/io-wq.c)
created by create_io_thread()?

So that every resource the threads used are credited to the process
of the vm.

Thanks
Lai