another day, another master merge

* master:
  Fix cycle dispute-coordinator <-> dispute-distribution  (#6489)
  Replace async-std with tokio in PVF subsystem (#6419)
  Guide changes 3 (#6520)
  Bump tokio from 1.22.0 to 1.24.1 (#6523)
  Fix flaky test in `dispute-coordinator` (#6524)
  Remove unused code (#6525)

Cargo.toml

@@ -27,7 +27,7 @@ tikv-jemallocator = "0.5.0"
 assert_cmd = "2.0.4"
 nix = "0.24.1"
 tempfile = "3.2.0"
-tokio = "1.22.0"
+tokio = "1.24.1"
 substrate-rpc-client = { git = "https://github.com/paritytech/substrate", branch = "master" }
 polkadot-core-primitives = { path = "core-primitives" }
 

node/core/candidate-validation/src/lib.rs

@@ -627,7 +627,8 @@ trait ValidationBackend {
 			self.validate_candidate(pvf.clone(), timeout, params.encode()).await;
 
 		// If we get an AmbiguousWorkerDeath error, retry once after a brief delay, on the
-		// assumption that the conditions that caused this error may have been transient.
+		// assumption that the conditions that caused this error may have been transient. Note that
+		// this error is only a result of execution itself and not of preparation.
 		if let Err(ValidationError::InvalidCandidate(WasmInvalidCandidate::AmbiguousWorkerDeath)) =
 			validation_result
 		{
@@ -676,12 +677,12 @@ impl ValidationBackend for ValidationHost {
 
 	async fn precheck_pvf(&mut self, pvf: Pvf) -> Result<Duration, PrepareError> {
 		let (tx, rx) = oneshot::channel();
-		if let Err(_) = self.precheck_pvf(pvf, tx).await {
+		if let Err(err) = self.precheck_pvf(pvf, tx).await {
 			// Return an IO error if there was an error communicating with the host.
-			return Err(PrepareError::IoErr)
+			return Err(PrepareError::IoErr(err))
 		}
 
-		let precheck_result = rx.await.or(Err(PrepareError::IoErr))?;
+		let precheck_result = rx.await.map_err(|err| PrepareError::IoErr(err.to_string()))?;
 
 		precheck_result
 	}

node/core/candidate-validation/src/tests.rs

@@ -1053,5 +1053,5 @@ fn precheck_properly_classifies_outcomes() {
 	inner(Err(PrepareError::Panic("baz".to_owned())), PreCheckOutcome::Invalid);
 
 	inner(Err(PrepareError::TimedOut), PreCheckOutcome::Failed);
-	inner(Err(PrepareError::IoErr), PreCheckOutcome::Failed);
+	inner(Err(PrepareError::IoErr("fizz".to_owned())), PreCheckOutcome::Failed);
 }

node/core/dispute-coordinator/Cargo.toml

@@ -31,6 +31,7 @@ assert_matches = "1.4.0"
 test-helpers = { package = "polkadot-primitives-test-helpers", path = "../../../primitives/test-helpers" }
 futures-timer = "3.0.2"
 sp-application-crypto = { git = "https://github.com/paritytech/substrate", branch = "master" }
+sp-tracing = { git = "https://github.com/paritytech/substrate", branch = "master" }
 
 [features]
 # If not enabled, the dispute coordinator will do nothing.