Fix race condition in async `UtxoFuture` resolution #4348

tnull · 2026-01-26T16:16:46Z

Previously, we refactored the GossipVerifier to not require holding a
circular reference. As part of this, we moved to a model where the
UtxoFutures are now polled by the background processor which checks
for completion through get_and_clear_pending_msg_events.

However, as part of this refactor we introduced race-condition: as we
only held Weak references in PendingChecksContext and the
UtxoFuture was directly dropped by the GossipVerifier after calling
resolve, the actual data was dropped with the future and gone when the
background processor attempted to retrieve and apply it via
check_resolved_futures.

Here, we fix this issue by simply holding on to the state Arcs in a
separate pending_states Vec that is only pruned in
check_resolved_futures, ensuring any completed results are collected
first.

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lightning/src/routing/utxo.rs

TheBlueMatt · 2026-01-26T21:58:31Z

lightning/src/routing/utxo.rs

+			.read_only()
+			.channels()
+			.get(&valid_announcement.contents.short_channel_id)
+			.unwrap()


same here. the rustfmt behavior of treating things like as_ref().unwrap() as "equally important" as ".get(X) or ".features" makes this so hard to follow.

Still the same on the latest version?

lightning/src/routing/utxo.rs

tnull

Now switched to a much less invasive approach where we simply keep track of the pending future states Arcs in a separate Vec until the next call of check_resolved_futures, which will collect completed states and prune the data structures.

tnull · 2026-01-28T14:16:46Z

Whoops, seems there are still some more tests to fix, drafting again 🤭

Signed-off-by: Elias Rohrer <dev@tnull.de>

Previously, we refactored the `GossipVerifier` to not require holding a circular reference. As part of this, we moved to a model where the `UtxoFuture`s are now polled by the background processor which checks for completion through `get_and_clear_pending_msg_events`. However, as part of this refactor we introduced race-condition: as we only held `Weak` references in `PendingChecksContext` and the `UtxoFuture` was directly dropped by the `GossipVerifier` after calling `resolve`, the actual data was dropped with the future and gone when the background processor attempted to retrieve and apply it via `check_resolved_futures`. Here, we fix this issue by simply holding on to the `state` `Arc`s in a separate `pending_states` `Vec` that is only pruned in `check_resolved_futures`, ensuring any completed results are collected first. Signed-off-by: Elias Rohrer <dev@tnull.de>

tnull · 2026-01-28T14:28:15Z

Whoops, seems there are still some more tests to fix, drafting again 🤭

... and they're passing again.

codecov · 2026-01-28T17:29:01Z

Codecov Report

❌ Patch coverage is 92.06349% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.11%. Comparing base (9e91b2e) to head (0da4883).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/routing/utxo.rs	92.06%	23 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4348      +/-   ##
==========================================
+ Coverage   86.08%   86.11%   +0.02%     
==========================================
  Files         156      156              
  Lines      102428   102625     +197     
  Branches   102428   102625     +197     
==========================================
+ Hits        88179    88377     +198     
- Misses      11754    11755       +1     
+ Partials     2495     2493       -2

Flag	Coverage Δ
tests	`86.11% <92.06%> (+0.02%)`	⬆️

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TheBlueMatt

Bleh, don't love the extra vec but you're right that its much simpler and probably worth it. Feel free to squash (maybe with a few more rustfmt'isms fixed) and let's land this.

TheBlueMatt · 2026-01-28T18:51:44Z

lightning/src/routing/utxo.rs

+			.read_only()
+			.nodes()
+			.get(&node_id_1)
+			.unwrap()


These are also pretty borderline (there's a few more further down).

TheBlueMatt · 2026-01-28T18:52:26Z

lightning/src/routing/utxo.rs

+			.read_only()
+			.channels()
+			.get(&valid_announcement.contents.short_channel_id)
+			.unwrap()


Still the same on the latest version?

ldk-reviews-bot · 2026-01-28T18:53:26Z

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tnull marked this pull request as draft January 26, 2026 16:16

tnull force-pushed the 2026-01-fix-gossip-verification branch 2 times, most recently from 7c871f2 to 5c757b3 Compare January 26, 2026 16:18

TheBlueMatt reviewed Jan 26, 2026

View reviewed changes

tnull self-assigned this Jan 28, 2026

tnull added this to Weekly Goals Jan 28, 2026

tnull moved this to Goal: Merge in Weekly Goals Jan 28, 2026

tnull force-pushed the 2026-01-fix-gossip-verification branch from 5c757b3 to e3bf6a5 Compare January 28, 2026 13:53

tnull requested a review from TheBlueMatt January 28, 2026 13:54

tnull marked this pull request as ready for review January 28, 2026 13:54

tnull force-pushed the 2026-01-fix-gossip-verification branch 2 times, most recently from f672e27 to 7c08572 Compare January 28, 2026 13:57

tnull commented Jan 28, 2026

View reviewed changes

tnull added this to the 0.3 milestone Jan 28, 2026

tnull marked this pull request as draft January 28, 2026 14:16

tnull force-pushed the 2026-01-fix-gossip-verification branch from 7c08572 to 585fd56 Compare January 28, 2026 14:26

tnull added 3 commits January 28, 2026 15:27

Remove rustfmt::skip from utxo.rs

2875802

Signed-off-by: Elias Rohrer <dev@tnull.de>

f Address rustfmt comments

7cfc19c

tnull force-pushed the 2026-01-fix-gossip-verification branch from 585fd56 to 0da4883 Compare January 28, 2026 14:27

tnull marked this pull request as ready for review January 28, 2026 14:28

TheBlueMatt reviewed Jan 28, 2026

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Fix race condition in async UtxoFuture resolution #4348

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Fix race condition in async UtxoFuture resolution #4348

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Fix race condition in async `UtxoFuture` resolution #4348

Fix race condition in async `UtxoFuture` resolution #4348

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