PVF: Don't dispute on missing artifact #7011

mrcnski · 2023-04-05T16:16:30Z

PULL REQUEST

Overview

A dispute should never be raised if the local cache doesn't provide a certain artifact. You can not dispute based on this reason, as it is a local hardware issue and not related to the candidate to check.

Design

Currently we assume that if we prepared an artifact, it remains there on-disk until we prune it, i.e. we never check again if it's still there.

We can change it so that instead of artifact-not-found triggering a dispute, we retry once (like we do for AmbiguousWorkerDeath, except we don't dispute if it still doesn't work). And when enqueuing an execute job, we check for the artifact on-disk, and start preparation if not found.

Changes

Integration test (should fail without the following changes)
Check if artifact exists when executing, prepare if not
Return an internal error when file is missing
Retry once on internal errors
Document design (update impl guide)
Also snuck in a refactor of handle_execute_pvf...

Related issues

Closes #6959
Pre-requisite for paritytech/polkadot-sdk#685

A dispute should never be raised if the local cache doesn't provide a certain artifact. You can not dispute based on this reason, as it is a local hardware issue and not related to the candidate to check. Design: Currently we assume that if we prepared an artifact, it remains there on-disk until we prune it, i.e. we never check again if it's still there. We can change it so that instead of artifact-not-found triggering a dispute, we retry once (like we do for AmbiguousWorkerDeath, except we don't dispute if it still doesn't work). And when enqueuing an execute job, we check for the artifact on-disk, and start preparation if not found. Changes: - [x] Integration test (should fail without the following changes) - [x] Check if artifact exists when executing, prepare if not - [x] Return an internal error when file is missing - [x] Retry once on internal errors - [x] Document design (update impl guide)

node/core/pvf/src/execute/worker.rs

mrcnski · 2023-04-05T16:42:18Z

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

-			// Wait a brief delay before retrying.
-			futures_timer::Delay::new(PVF_EXECUTION_RETRY_DELAY).await;
+		// Allow one retry for each kind of error.
+		let mut num_internal_retries_left = 1;


Could make this higher, since this kind of error is probably the most likely to be transient.

eskimor · 2023-04-05T20:46:48Z

node/core/pvf/src/execute/worker.rs

@@ -359,7 +366,13 @@ fn validate_using_artifact(
 		//         [`executor_intf::prepare`].
 		executor.execute(artifact_path.as_ref(), params)
 	} {
-		Err(err) => return Response::format_invalid("execute", &err),
+		Err(err) =>
+			return if err.contains("failed to open file: No such file or directory") {


This really requires a refactor changing the error type to something sensible, like an enum. Matching on a string is way too error prone. Something changes the message, localization, ....

Very likely to come from substrate, it's full of string errors. I agree that matching against strings is no-go, but otherwise we'd have to halt the pr.

This really requires a refactor changing the error type to something sensible, like an enum

Vote up, I've already raised that concern somewhere... Many errors coming from Substrate are not sensible at all. Also agree that string matching makes no good.

@mrcnski a (probably stupid) idea: until we have an enum error from Substrate, would it be better not to rely on its string errors but to check for the file existence ourselves? Should be simple enough. Of course, it introduces a race condition, but still better than parsing strings. Also, nobody guarantees that the file persists between the moments when it is open and when it is read, so that kind of race condition already exists anyway.

Yeah, it comes from Substrate. Didn't think about localization. 😬 I considered just treating RuntimeConstruction itself as an internal error, but seems it's also used for some case where wasm runs out of memory, which would be a problem with the PVF itself. link

Checking for the file existence seems sensible to me...

Problems with the PVF itself we agreed are also no reason to raise a dispute, since we have pre-checking enabled. Basically any error that is independent of the candidate at hand should not be cause for a dispute.

Let's in any case create a ticket for fixing those string errors - or at least the one in question right now.

Looks like "output exceeds bounds of wasm memory" should not be an issue with runtime construction, but is actually indicative of a malicious PVF. And I think this would get past pre-checking, since that just compiles and doesn't execute.

https://github.com/paritytech/substrate/blob/master/client/executor/wasmtime/src/runtime.rs#L772-L780

// Do a length check before allocating. The returned output should not be bigger than the // available WASM memory. Otherwise, a malicious parachain can trigger a large allocation, // potentially causing memory exhaustion. // // Get the size of the WASM memory in bytes. let memory_size = ctx.as_context().data().memory().data_size(ctx); if checked_range(output_ptr as usize, output_len as usize, memory_size).is_none() { Err(WasmError::Other("output exceeds bounds of wasm memory".into()))? }

(I used WasmError::Other here to match the other errors in the file, without realizing it gets converted to RuntimeConstruction. 🤷‍♂️)

Anyway, basically, this one "output exceeds bounds of wasm memory" case is deterministic and we should definitely vote against. If we gave it a new separate enum in Substrate, then we could treat the existing RuntimeConstruction as an internal error.

Raised a small fix for the output-bounds case here, but I'm still not confident that RuntimeConstruction is always a transient error and don't think we should use it. Unless we treat it as a new "possibly transient" case, meaning we retry and dispute if it happens again. 🤷‍♂️

For the file-not-found case, there is not a clear way to fix the error story on the Substrate side. Just having another check here for file existence should be enough.

I am fine with the check, please reference the substrate issue though in a comment. This way, readers understand why we did it this way and we can reevaluate once the issue is fixed.

node/core/pvf/src/execute/worker.rs

mrcnski · 2023-04-19T07:27:03Z

Ready for another review. :) (Don't think we can do much about the Substrate error for now.)

slumber · 2023-04-19T13:00:54Z

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

@@ -691,38 +691,54 @@ trait ValidationBackend {



Updating candidate-validation tests would not harm

mrcnski · 2023-04-19T16:37:53Z

bot merge

paritytech-processbot · 2023-04-19T16:38:04Z

Error: Statuses failed for b450803

mrcnski · 2023-04-20T08:30:39Z

bot rebase

…-artifact

paritytech-processbot · 2023-04-20T08:30:47Z

Rebased

mrcnski · 2023-04-20T13:38:23Z

bot merge

* master: (30 commits) update rocksdb to 0.20.1 (#7113) Reduce base proof size weight component to zero (#7081) PVF: Move PVF workers into separate crate (#7101) Companion for #13923 (#7111) update safe call filter (#7080) PVF: Don't dispute on missing artifact (#7011) XCM: Properly set the pricing for the DMP router (#6843) pvf: Update docs for PVF artifacts (#6551) Bump syn from 2.0.14 to 2.0.15 (#7093) Companion for substrate#13771 (#6983) Added Dwellir Nigeria bootnodes. (#7097) Companion for Substrate #13889 (#7063) Switch to DNS name based bootnodes for Rococo (#7040) companion for substrate#13883 (#7059) [xcm] Added `UnpaidExecution` instruction to `UnpaidRemoteExporter` (#7091) Bump serde_json from 1.0.85 to 1.0.96 (#7072) Bump hex-literal from 0.3.4 to 0.4.1 (#7071) Small simplification (#7089) [XCM - UnpaidRemoteExporter] Remove unreachable code (#7088) sync versions with current release (#7083) ...

* master: (39 commits) malus: dont panic on missing validation data (#6952) Offences Migration v1: Removes `ReportsByKindIndex` (#7114) Fix stalling dispute coordinator. (#7125) Fix rolling session window (#7126) [ci] Update buildah command and version (#7128) Bump assigned_slots params (#6991) XCM: Remote account converter (#6662) Rework `dispute-coordinator` to use `RuntimeInfo` for obtaining session information instead of `RollingSessionWindow` (#6968) Revert default proof size back to 64 KB (#7115) update rocksdb to 0.20.1 (#7113) Reduce base proof size weight component to zero (#7081) PVF: Move PVF workers into separate crate (#7101) Companion for #13923 (#7111) update safe call filter (#7080) PVF: Don't dispute on missing artifact (#7011) XCM: Properly set the pricing for the DMP router (#6843) pvf: Update docs for PVF artifacts (#6551) Bump syn from 2.0.14 to 2.0.15 (#7093) Companion for substrate#13771 (#6983) Added Dwellir Nigeria bootnodes. (#7097) ...

mrcnski requested review from bkchr, slumber and s0me0ne-unkn0wn April 5, 2023 16:16

mrcnski commented Apr 5, 2023

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node/core/pvf/src/execute/worker.rs Outdated Show resolved Hide resolved

Add some context to wasm error message (it is quite long)

6fa0046

mrcnski force-pushed the mrcnski/pvf-missing-artifact branch from d043a32 to 6fa0046 Compare April 5, 2023 16:22

Fix impl guide

d1a3050

mrcnski commented Apr 5, 2023

View reviewed changes

mrcnski requested a review from eskimor April 5, 2023 16:44

eskimor reviewed Apr 5, 2023

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Add check for missing/inaccessible file

5982b8b

eskimor reviewed Apr 7, 2023

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node/core/pvf/src/execute/worker.rs Show resolved Hide resolved

This was referenced Apr 7, 2023

PVF host: sandbox/harden worker process paritytech/polkadot-sdk#882

Closed

Executor: Replace string errors with full source error paritytech/substrate#13860

Open

Add comment referencing Substrate issue

ff77e2a

mrcnski requested a review from eskimor April 10, 2023 15:10

This was referenced Apr 10, 2023

PVF: Add a new class of "possibly invalid" errors paritytech/polkadot-sdk#660

Closed

PVF: Throw error if worker process cannot spawn necessary threads paritytech/polkadot-sdk#659

Open

eskimor approved these changes Apr 19, 2023

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slumber approved these changes Apr 19, 2023

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Add test for retrying internal errors

b450803

Merge remote-tracking branch 'origin/master' into mrcnski/pvf-missing…

9259f72

…-artifact

paritytech-processbot bot merged commit 67278e0 into master Apr 20, 2023

paritytech-processbot bot deleted the mrcnski/pvf-missing-artifact branch April 20, 2023 13:38

mrcnski self-assigned this May 15, 2023

github-actions bot mentioned this pull request Jun 15, 2023

Update substrate/polkadot/cumulus from v0.9.40 to v0.9.43 moonbeam-foundation/moonbeam#2354

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PVF: Don't dispute on missing artifact #7011

PVF: Don't dispute on missing artifact #7011

mrcnski commented Apr 5, 2023 •

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mrcnski commented Apr 19, 2023

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mrcnski commented Apr 20, 2023

PVF: Don't dispute on missing artifact #7011

PVF: Don't dispute on missing artifact #7011

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mrcnski commented Apr 5, 2023 • edited Loading

PULL REQUEST

Overview

Design

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Related issues

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mrcnski commented Apr 19, 2023

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mrcnski commented Apr 5, 2023 •

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