backport: fix potential sql tx exhaustion

[ziggie1984]

Backports #10428

[gemini-code-assist]

Summary of Changes

Hello @ziggie1984, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a potential deadlock and SQL transaction exhaustion issue by carefully reordering the acquisition of a mutex lock relative to database transactions. Previously, taking a mutex lock within a transaction could lead to a situation where all transactions became blocked, causing a deadlock. The changes ensure that the cacheMu read lock is acquired before the database transaction begins and released after it completes, establishing a consistent lock ordering and significantly improving the stability and reliability of database operations.

Highlights

• Deadlock Prevention: Addresses a critical deadlock scenario where acquiring a mutex lock inside a database transaction could block all transactions waiting for the mutex, potentially leading to transaction exhaustion.
• Consistent Lock Ordering: Ensures a consistent lock ordering (cacheMu -> DB) by acquiring the cacheMu read lock before initiating the database transaction, preventing race conditions and deadlocks.
• Refactored Lock Management: The cacheMu.RLock() and cacheMu.RUnlock() calls are now managed outside the transaction execution blocks in fetchNextChanUpdateBatch and ChanUpdatesInHorizon functions, simplifying the locking logic within transactions.

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[gemini-code-assist]

Code Review

This pull request addresses a potential deadlock issue in both the kv_store and sql_store implementations by ensuring a consistent lock ordering. The change moves the acquisition of cacheMu's read lock to before the database transaction begins, preventing a situation where the database lock is held while waiting for the mutex, which could lead to a deadlock with write operations that acquire the locks in the opposite order. The implementation in both kv_store.go and sql_store.go is correct and effectively resolves the potential for transaction exhaustion and deadlocks. The code changes are clean, well-commented, and I have no further suggestions for improvement.

[yyforyongyu]

Can you confirm the flake is unrelated? From this build, https://github.com/lightningnetwork/lnd/actions/runs/20068530441/job/57563704057?pr=10429

I see permanently failed with no route: no_route in the log.

[ziggie1984]

yes they are unrelated, going to open a PR which fixes this race.

See: #10440

[yyforyongyu]

LGTM🥇