PR feedback & comment cleanup

bin/propolis-server/src/lib/vm/objects.rs

@@ -267,7 +267,7 @@ impl VmObjectsLocked {
         // that all devices resume before any vCPUs do.
         self.resume_kernel_vm();
         self.resume_devices();
-        self.vcpu_tasks.resume_all();
+        self.resume_vcpus();
     }
 
     /// Resumes this VM's vCPU tasks.
@@ -276,7 +276,7 @@ impl VmObjectsLocked {
     /// needs fine-grained control over the order in which devices and vCPUs
     /// start. When pausing and resuming a VM that's already been started, use
     /// [`Self::pause`] and [`Self::resume`] instead.
-    pub(crate) async fn resume_vcpus(&mut self) {
+    pub(crate) fn resume_vcpus(&mut self) {
         self.vcpu_tasks.resume_all();
     }
 
@@ -310,7 +310,7 @@ impl VmObjectsLocked {
         // Resume devices so they're ready to do more work, then resume
         // vCPUs.
         self.resume_devices();
-        self.vcpu_tasks.resume_all();
+        self.resume_vcpus();
     }
 
     /// Pauses all of a VM's devices.

bin/propolis-server/src/lib/vm/state_driver.rs

@@ -536,11 +536,12 @@ impl StateDriver {
 
         // The start sequence is arranged so that calls to block backends can be
         // interleaved with processing of requests from the external request
-        // queue. This allows Nexus to reconfigure Crucible volumes while they
-        // are being activated, which is necessary to unwedge activations that
-        // are targeting a downstairs that became invalid between the time Nexus
-        // passed its address to a VM and the time the VM actually tried to
-        // connect to it.
+        // queue. This allows Nexus to reconfigure Crucible backends while they
+        // are being activated, which can be necessary if the VM's original
+        // specification specifies a Crucible downstairs server that is offline
+        // or unavailable. (Downstairs instances can disappear at any time,
+        // e.g. due to sled failure, so these configurations aren't necessarily
+        // client errors.)
         //
         // Before getting into any of that, handle the synchronous portions of
         // VM startup. First, ensure that the kernel VM and all its associated
@@ -584,7 +585,11 @@ impl StateDriver {
                 info!(log, "starting block backend {}", name);
                 let res = backend.start().await;
                 if let Err(e) = &res {
-                    error!(log, "startup failed for {}: {:?}", name, e);
+                    error!(
+                        log,
+                        "startup failed for block backend {}: {:?}", name, e
+                    );
+
                     return res;
                 }
             }
@@ -614,7 +619,7 @@ impl StateDriver {
                 res = &mut block_backend_fut => {
                     if res.is_ok() {
                         let objects = &self.objects;
-                        objects.lock_exclusive().await.resume_vcpus().await;
+                        objects.lock_exclusive().await.resume_vcpus();
                         self.publish_steady_state(InstanceState::Running);
                         info!(&self.log, "VM successfully started");
                     }

phd-tests/tests/src/crucible/smoke.rs

@@ -108,12 +108,16 @@ async fn vcr_replace_during_start_test(ctx: &Framework) {
         5,
     );
 
+    // Configure the disk so that when the VM starts, it will have an invalid
+    // downstairs address.
     let spec = config.vm_spec(ctx).await?;
     let disk_hdl =
         spec.get_disk_by_device_name(DATA_DISK_NAME).cloned().unwrap();
     let disk = disk_hdl.as_crucible().unwrap();
     disk.enable_vcr_black_hole();
 
+    // Try to start the VM, but don't wait for it to boot; it should get stuck
+    // while activating using an invalid downstairs address.
     let mut vm = ctx.spawn_vm_with_spec(spec, None).await?;
     vm.launch().await?;
 
@@ -125,9 +129,17 @@ async fn vcr_replace_during_start_test(ctx: &Framework) {
         .await
         .unwrap_err();
 
+    // Fix the disk's downstairs address and send a replacement request. This
+    // should be processed and should allow the VM to boot.
     disk.disable_vcr_black_hole();
     disk.set_generation(2);
     vm.replace_crucible_vcr(disk).await?;
-
     vm.wait_to_boot().await?;
+
+    assert_eq!(vm.get().await?.instance.state, InstanceState::Running);
+
+    // VCR replacements should continue to be accepted now that the instance is
+    // running.
+    disk.set_generation(3);
+    vm.replace_crucible_vcr(disk).await?;
 }