KVM: Move VM's worker kthreads back to the original cgroup before exiting.
authorVipin Sharma <vipinsh@google.com>
Tue, 22 Feb 2022 05:48:48 +0000 (05:48 +0000)
committerPaolo Bonzini <pbonzini@redhat.com>
Fri, 25 Feb 2022 13:20:14 +0000 (08:20 -0500)
commite45cce30eade14cdc1a98a9c1cd51f3294e3597b
treea8f1fc422944339c98ca664b5acda407ad68d56b
parent0b8934d3a93ff3b89f7c2dbcc00de88cf5ae0d7e
KVM: Move VM's worker kthreads back to the original cgroup before exiting.

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

KVM terminates the worker kthreads by calling kthread_stop() which waits
on the 'exited' completion, triggered by exit_mm(), via mm_release(), in
do_exit() during the kthread's exit.  However, these kthreads are
removed from the cgroup using the cgroup_exit() which happens after the
exit_mm(). Therefore, A VM process can terminate in between the
exit_mm() and cgroup_exit() calls, leaving only worker kthreads in the
cgroup.

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

Signed-off-by: Vipin Sharma <vipinsh@google.com>
Suggested-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220222054848.563321-1-vipinsh@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
virt/kvm/kvm_main.c