On Tue, Dec 28, 2021 at 9:17 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > On Wed, Dec 22, 2021, Vipin Sharma wrote: > > diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c > > index 81c9e0685948..81d4b2f2acf0 100644 > > --- a/kernel/cgroup/cgroup-v1.c > > +++ b/kernel/cgroup/cgroup-v1.c > > int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk) > > @@ -58,6 +60,9 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk) > > struct cgroup_root *root; > > int retval = 0; > > > > + if (!from) > > + from = kthreadd_task; > > Rather than sully cgroup_attach_task_all() with this behavior, can't KVM do > > cgroup_attach_task_all(current->real_parent, current) > > since AFAICT real_parent is guaranteed to point at kthreadd_task. > Thanks for the "real_parent" suggestion. This is much cleaner and better than changing cgroup logic. I will make this change. > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > > index b0f7e6eb00ff..f7504578c374 100644 > > --- a/virt/kvm/kvm_main.c > > +++ b/virt/kvm/kvm_main.c > > @@ -5793,6 +5793,19 @@ static int kvm_vm_worker_thread(void *context) > > if (!kthread_should_stop()) > > err = thread_fn(kvm, data); > > > > +out: > > + /* > > + * We need to move the kthread back to its original cgroups, so that it > > Please state what is being done, not what "needs" to be done. The need to do > something is implicit, otherwise we wouldn't be doing it. > I will update the statement. Thanks. > > + * doesn't linger in the cgroups of the user process after the user > > + * process has already terminated. > > + * > > + * kthread_stop() waits on 'exited' completion condition which is set > > + * in exit_mm(), via mm_release(), in do_exit(). However, kthread > > + * is removed from cgroups in the cgroup_exit() which is called after > > + * exit_mm(). This causes lingering of kthreads in cgroups after main > > + * VM process has finished. > > + */ > > + WARN_ON(cgroup_attach_task_all(NULL, current)); > > This should not WARN, cgroup_attach_task_all() needs to perform allocations and > will fail with -ENOMEM even in the absense of kernel bugs. > I will remove WARN_ON and print an error using kvm_err(), it will be similar to the earlier call of cgroup_attach_task_all() in the same function. Thanks
