On Fri, Sep 29, 2017 at 12:01:24PM +0200, Paolo Bonzini wrote: > > Does this mean whenever we get a page fault in a RCU read-side critical > > section, we may hit this? > > > > Could we simply avoid to schedule() in kvm_async_pf_task_wait() if the > > fault process is in a RCU read-side critical section as follow? > > > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > > index aa60a08b65b1..291ea13b23d2 100644 > > --- a/arch/x86/kernel/kvm.c > > +++ b/arch/x86/kernel/kvm.c > > @@ -140,7 +140,7 @@ void kvm_async_pf_task_wait(u32 token) > > > > n.token = token; > > n.cpu = smp_processor_id(); > > - n.halted = is_idle_task(current) || preempt_count() > 1; > > + n.halted = is_idle_task(current) || preempt_count() > 1 || rcu_preempt_depth(); > > init_swait_queue_head(&n.wq); > > hlist_add_head(&n.link, &b->list); > > raw_spin_unlock(&b->lock); > > > > (Add KVM folks and list Cced) > > Yes, that would work. Mind to send it as a proper patch? I'm confused, why would we do an ASYNC PF at all here? Thing is, a printk() shouldn't trigger a major fault _ever_. At worst it triggers something like a vmalloc minor fault. And I'm thinking we should not do the whole ASYNC machinery for minor faults.
