Acquire SRCU outside of irqfds.lock so that the locking is symmetrical, and add a comment explaining why on earth KVM holds SRCU for so long.
Signed-off-by: Sean Christopherson seanjc@google.com --- virt/kvm/eventfd.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-)
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c index 39e42b19d9f7..42c02c35e542 100644 --- a/virt/kvm/eventfd.c +++ b/virt/kvm/eventfd.c @@ -401,6 +401,18 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) */ init_waitqueue_func_entry(&irqfd->wait, irqfd_wakeup);
+ /* + * Set the irqfd routing and add it to KVM's list before registering + * the irqfd with the eventfd, so that the routing information is valid + * and stays valid, e.g. if there are GSI routing changes, prior to + * making the irqfd visible, i.e. before it might be signaled. + * + * Note, holding SRCU ensures a stable read of routing information, and + * also prevents irqfd_shutdown() from freeing the irqfd before it's + * fully initialized. + */ + idx = srcu_read_lock(&kvm->irq_srcu); + spin_lock_irq(&kvm->irqfds.lock);
ret = 0; @@ -409,11 +421,9 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) continue; /* This fd is used for another irq already. */ ret = -EBUSY; - spin_unlock_irq(&kvm->irqfds.lock); - goto fail; + goto fail_duplicate; }
- idx = srcu_read_lock(&kvm->irq_srcu); irqfd_update(kvm, irqfd);
list_add_tail(&irqfd->list, &kvm->irqfds.items); @@ -449,6 +459,9 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) srcu_read_unlock(&kvm->irq_srcu, idx); return 0;
+fail_duplicate: + spin_unlock_irq(&kvm->irqfds.lock); + srcu_read_unlock(&kvm->irq_srcu, idx); fail: if (irqfd->resampler) irqfd_resampler_shutdown(irqfd);