On 02/09/21 21:21, Sean Christopherson wrote:
+ if (!matched) { + ... + spin_lock(&kvm->arch.pvclock_gtod_sync_lock); + kvm->arch.nr_vcpus_matched_tsc = 0; + } else if (!already_matched) { + spin_lock(&kvm->arch.pvclock_gtod_sync_lock); + kvm->arch.nr_vcpus_matched_tsc++; + } + + kvm_track_tsc_matching(vcpu); + spin_unlock(&kvm->arch.pvclock_gtod_sync_lock);This unlock is imbalanced if matched and already_matched are both true. It's not immediately obvious that that_can't_ happen, and if it truly can't happen then conditionally locking is pointless (because it's not actually conditional).
This is IMO another reason to unify tsc_write_lock and pvclock_gtod_sync_lock. The chances of contention are pretty slim. As soon as I sort out the next -rc3 pull request I'll send out my version of Oliver's patches.
Thanks, Paolo
