On 2017年12月19日 18:41, Paolo Bonzini wrote: > On 19/12/2017 07:35, Lan Tianyu wrote: >> On 2017年12月18日 16:50, Paolo Bonzini wrote: >>> On 18/12/2017 09:30, David Hildenbrand wrote: >>>> The ugly thing in kvm_irqfd_assign() is that we access irqfd without >>>> holding a lock. I think that should rather be fixed than working around >>>> that issue. (e.g. lock() -> lookup again -> verify still in list -> >>>> unlock()) >>> >>> I wonder if it's even simpler: >>> >>> diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c >>> index f2ac53ab8243..17ed298bd66f 100644 >>> --- a/virt/kvm/eventfd.c >>> +++ b/virt/kvm/eventfd.c >>> @@ -387,7 +387,6 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) >>> >>> idx = srcu_read_lock(&kvm->irq_srcu); >>> irqfd_update(kvm, irqfd); >>> - srcu_read_unlock(&kvm->irq_srcu, idx); >>> >>> list_add_tail(&irqfd->list, &kvm->irqfds.items); >>> >>> @@ -420,10 +419,12 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) >>> irqfd->consumer.token, ret); >>> } >>> #endif >>> + srcu_read_unlock(&kvm->irq_srcu, idx); >>> >>> return 0; >>> >>> fail: >>> + /* irq_srcu is *not* held here. */ >>> if (irqfd->resampler) >>> irqfd_resampler_shutdown(irqfd); >>> >>> >> >> Hi Paolo: >> This patch still can't prevent from freeing struct irqfd in >> irq_shutdown() during assign irqfd. Once irqfd is added to >> kvm->irqfds.items list, deassign path can get irqfd and free it. > > You're right, that also has to be protected by SRCU. So a new bool is > needed (probably "active" more than "initialized") in order to replace > list_del_init with list_del_rcu. > Adding new flag is sufficient to fix the crash issue. All list operations for kvm->irqfds.items list are already under protection kvm->irqfds.lock. Do you mean we should use list_add/del_rcu for kvm->irqfds.items? -- Best regards Tianyu Lan
