{ "number": 36525, "input_hash": "df1f7122cce5ecca", "model": "ledger", "prompt_hash": null, "created": "2026-10-30T01:14:19+00:00", "result": { "summary": "Protects block template access in the mining interface implementation with a mutex to serialize concurrent IPC worker thread operations. Adds an `m_total_fees` field to `CBlockTemplate` along with a corresponding `getTotalFees()` getter exposed over IPC. Modifies `WaitAndCreateNewBlock` to accept the previous block hash and fee values by value rather than inspecting the template pointer directly, allowing callers to release the template lock before waiting.", "problem": "Concurrent IPC worker threads can trigger data races when one thread modifies an active `CBlockTemplate` during `submitSolution()` while another thread reads from it. Furthermore, external IPC mining clients requiring total fee figures have to repeatedly retrieve and sum individual transaction fees across the IPC boundary.", "card": "This PR resolves a multithreading data race in the mining IPC interface where concurrent worker threads access m_block_template simultaneously, such as when submitSolution modifies a template while another call reads it. It guards template accesses inside BlockTemplateImpl with a mutex and updates WaitAndCreateNewBlock so the template lock can be released before entering the wait loop. In addition, it caches total fees on CBlockTemplate and introduces a getTotalFees() IPC method so clients do not have to aggregate per-transaction fees. The primary motivation is fixing issue #36515.", "evidence": [ "Commit 4774cf1de6 and PR description state that IPC calls on different worker threads can race when submitSolution modifies a template while another call reads it, fixing issue #36515." ], "scope_notes": "", "changed_since_previous": "Added a Python functional test (run_concurrent_template_access_test in interface_ipc_mining.py) that exercises concurrent reads and submitSolution operations across separate Cap'n Proto worker threads.", "thread": { "last_event_at": "2026-10-29T09:19:02Z", "events": 22, "head_sha": "cbadeff334f182086538d7483dc1146c559859e6", "schema_floor": 2, "schema": 2 }, "waiting_on": [ { "at": "2026-10-29", "id": "c:6491583234", "on": "reviewer", "url": "https://github.com/bitcoin/bitcoin/pull/36525#issuecomment-6491583234", "what": "sedited to respond to benchmark results and proposed deferral of making template const" } ], "risk": { "level": "medium", "touches": [ "other" ], "why": "Mistakes in mutex scoping or lock inversion in BlockTemplateImpl could deadlock IPC mining worker threads or cause mining block submissions to stall." }, "discussion": { "author_status": "last statement processed 2026-10-29", "open_concerns": [], "resolved_concerns": [ "ismaelsadeeq: Is returning a vector of individual fees redundant now that total fees can be returned directly? (answered by Sjors 2026-10-15)", "ismaelsadeeq: Add a concurrent template access functional test to exercise the data race under TSAN (accepted by ismaelsadeeq 2026-10-16)", "enirox001: include the concurrent template access test as it consistently caught the regression under TSAN (accepted by enirox001 2026-10-16)", "sedited: Make m_block_template non-mutating/const instead of protecting it with a mutex (answered by Sjors 2026-10-29)", "ismaelsadeeq: Return the block copy after applying the solution (answered by Sjors 2026-10-25)" ] }, "reviewability": { "state": "Ready", "label": "Ready", "reason": "Nothing known that would invalidate a review now." }, "agreement": { "state": "Strong", "summary": "Strong: substantive support, no open objection (ismaelsadeeq, enirox001)", "reason": "Sjors benchmarked making the block template immutable and returning the full block in submitSolution(), identifying an IPC single-thread latency penalty in sv2-tp and recommending deferring immutability until IPC improvements land.", "evidence": [ "w0xlt: Concept ACK \u2014 Concept ACK", "ismaelsadeeq: ACK \u2014 ACK 4774cf1de6a4670323686bf93beb93035b3f6dad", "enirox001: ACK \u2014 Fixes a data race between IPC calls modifying and reading a template, adds getTotalFees IPC method, tested with TSAN", "ismaelsadeeq: ACK \u2014 reACK cbadeff334f182086538d7483dc1146c559859e6", "enirox001: ACK \u2014 reACK https://github.com/bitcoin/bitcoin/pull/36525/changes/cbadeff334f182086538d7483dc1146c559859e6", "w0xlt: ACK \u2014 ACK cbadeff334" ], "objections": [ { "reviewer": "ismaelsadeeq", "association": "MEMBER", "type": "question", "kind": "interface", "harm": "", "request": "", "question": "Is returning a vector of individual fees redundant now that total fees can be returned directly?", "text": "Is returning a vector of individual fees redundant now that total fees can be returned directly?", "clears_with": "answer", "blocking": false, "status": "answered", "status_note": "Sjors explained the vector is kept for compatibility with getblocktemplate and possible miner dashboard use cases", "cleared": true, "author_replied": true, "others_replied": false, "fix_pushed": false, "replies": [ "c:6185087776" ], "evidence": "2026-10-15: 'It makes sense to return it so they don't have to sum them, so the vector one is now redundant?'", "url": "https://github.com/bitcoin/bitcoin/pull/36525#pullrequestreview-5528160495", "id": "r:5528160495", "at": "2026-10-15", "status_at": "2026-10-15", "status_by": "Sjors", "resolution_evidence": "2026-10-15: Sjors: 'Providing the total and individual via IPC is trivial, so I think we should keep it.'", "pin": null, "from_schema": 2 }, { "reviewer": "ismaelsadeeq", "association": "MEMBER", "type": "suggestion", "kind": "safety", "harm": "", "request": "Add a concurrent template access functional test to exercise the data race under TSAN", "question": "", "text": "Add a concurrent template access functional test to exercise the data race under TSAN", "clears_with": "answer", "blocking": false, "status": "accepted", "status_note": "author added test in c:6205291499 and reviewer reACKed", "cleared": true, "author_replied": true, "others_replied": false, "fix_pushed": true, "replies": [ "c:6185555791", "c:6205291499" ], "evidence": "2026-10-15: 'See minimal test that fails on our tsan functional tests.'", "url": "https://github.com/bitcoin/bitcoin/pull/36525#pullrequestreview-5528160495", "id": "r:5528160495#2", "at": "2026-10-15", "status_at": "2026-10-16", "status_by": "ismaelsadeeq", "resolution_evidence": "2026-10-16: ismaelsadeeq: 'reACK cbadeff334f182086538d7483dc1146c559859e6'", "pin": null, "from_schema": 2 }, { "reviewer": "enirox001", "association": "CONTRIBUTOR", "type": "suggestion", "kind": "correctness", "harm": "", "request": "include the concurrent template access test as it consistently caught the regression under TSAN", "question": "", "text": "include the concurrent template access test as it consistently caught the regression under TSAN", "clears_with": "answer", "blocking": false, "status": "accepted", "status_note": "author added test in c:6205291499 and reviewer reACKed", "cleared": true, "author_replied": true, "others_replied": false, "fix_pushed": true, "replies": [ "c:6205291499" ], "evidence": "2026-10-15: 'I think the test is worth including. even though reproduction depends on scheduling, it consistently caught the regression on my machine'", "url": "https://github.com/bitcoin/bitcoin/pull/36525#pullrequestreview-5530690658", "id": "r:5530690658", "at": "2026-10-15", "status_at": "2026-10-16", "status_by": "enirox001", "resolution_evidence": "2026-10-16: enirox001: 'reACK https://github.com/bitcoin/bitcoin/pull/36525/changes/cbadeff334f182086538d7483dc1146c559859e6'", "pin": null, "from_schema": 2 }, { "reviewer": "sedited", "association": "MEMBER", "type": "suggestion", "kind": "approach", "harm": "", "request": "Make m_block_template non-mutating/const instead of protecting it with a mutex", "question": "", "text": "Make m_block_template non-mutating/const instead of protecting it with a mutex", "clears_with": "answer", "blocking": false, "status": "answered", "status_note": "author benchmarked the immutable approach, found sv2-tp latency regressions due to IPC bottlenecks, and suggested deferring", "cleared": true, "author_replied": true, "others_replied": true, "fix_pushed": false, "replies": [ "c:6380417140", "c:6408317995", "c:6491583234", "c:6492816419", "c:6313711072", "c:6321446193" ], "evidence": "2026-10-21: 'Might it be preferable to make m_block_template non-mutating? Do users of the interface even need the mutated template after submitting?'", "url": "https://github.com/bitcoin/bitcoin/pull/36525#issuecomment-6313228827", "id": "c:6313228827", "at": "2026-10-21", "status_at": "2026-10-29", "status_by": "Sjors", "resolution_evidence": "2026-10-29: Sjors: 'So my preference would be to defer making CBlockTemplate const until after these improvements land.'", "pin": null, "from_schema": 2 }, { "reviewer": "ismaelsadeeq", "association": "MEMBER", "type": "suggestion", "kind": "interface", "harm": "", "request": "Return the block copy after applying the solution", "question": "", "text": "Return the block copy after applying the solution", "clears_with": "answer", "blocking": false, "status": "answered", "status_note": "author explained clients intentionally wait 1 second before requesting it so as not to distract the node", "cleared": true, "author_replied": true, "others_replied": false, "fix_pushed": false, "replies": [ "c:6396275706", "c:6491583234" ], "evidence": "2026-10-25: 'Could we just return the block copy after applying the solution?'", "url": "https://github.com/bitcoin/bitcoin/pull/36525#issuecomment-6394296261", "id": "c:6394296261", "at": "2026-10-25", "status_at": "2026-10-25", "status_by": "Sjors", "resolution_evidence": "2026-10-25: Sjors: 'in theory yes, but clients intentionally wait 1 second before requesting it.'", "pin": null, "from_schema": 2 } ], "support": [ { "reviewer": "w0xlt", "reason": "Concept ACK", "substantive": false, "verdict": "Concept ACK", "id": "c:6185669122", "url": "https://github.com/bitcoin/bitcoin/pull/36525#issuecomment-6185669122", "at": "2026-10-15", "association": "CONTRIBUTOR", "evidence": "none", "areas": [] }, { "reviewer": "ismaelsadeeq", "reason": "ACK 4774cf1de6a4670323686bf93beb93035b3f6dad", "substantive": true, "verdict": "ACK", "id": "r:5528160495", "url": "https://github.com/bitcoin/bitcoin/pull/36525#pullrequestreview-5528160495", "at": "2026-10-15", "association": "MEMBER", "evidence": "read", "areas": [] }, { "reviewer": "enirox001", "reason": "Fixes a data race between IPC calls modifying and reading a template, adds getTotalFees IPC method, tested with TSAN", "substantive": true, "verdict": "ACK", "id": "r:5530690658", "url": "https://github.com/bitcoin/bitcoin/pull/36525#pullrequestreview-5530690658", "at": "2026-10-15", "association": "CONTRIBUTOR", "evidence": "tested", "areas": [] }, { "reviewer": "ismaelsadeeq", "reason": "reACK cbadeff334f182086538d7483dc1146c559859e6", "substantive": false, "verdict": "ACK", "id": "r:5543130614", "url": "https://github.com/bitcoin/bitcoin/pull/36525#pullrequestreview-5543130614", "at": "2026-10-16", "association": "MEMBER", "evidence": "none", "areas": [] }, { "reviewer": "enirox001", "reason": "reACK https://github.com/bitcoin/bitcoin/pull/36525/changes/cbadeff334f182086538d7483dc1146c559859e6", "substantive": false, "verdict": "ACK", "id": "r:5545791068", "url": "https://github.com/bitcoin/bitcoin/pull/36525#pullrequestreview-5545791068", "at": "2026-10-16", "association": "CONTRIBUTOR", "evidence": "none", "areas": [] }, { "reviewer": "w0xlt", "reason": "ACK cbadeff334", "substantive": false, "verdict": "ACK", "id": "r:5592756558", "url": "https://github.com/bitcoin/bitcoin/pull/36525#pullrequestreview-5592756558", "at": "2026-10-20", "association": "CONTRIBUTOR", "evidence": "none", "areas": [] } ], "participants": [ { "login": "enirox001", "stance": "support", "note": "ACKed with TSAN testing, supported including the test, and reACKed after the test was added", "association": "CONTRIBUTOR", "comments": 2, "first": "2026-10-15", "last": "2026-10-16" }, { "login": "ismaelsadeeq", "stance": "support", "note": "ACKed, proposed a functional test, reACKed once the test was included, and suggested returning the block copy after applying the solution", "association": "MEMBER", "comments": 5, "first": "2026-10-15", "last": "2026-10-25" }, { "login": "w0xlt", "stance": "support", "note": "ACKed with doc nits, and supported the suggestion to make m_block_template non-mutating", "association": "CONTRIBUTOR", "comments": 3, "first": "2026-10-15", "last": "2026-10-21" }, { "login": "sedited", "stance": "question", "note": "suggested making m_block_template non-mutating instead of adding mutex protection, and pushed back on whether block copying distraction is a valid concern", "association": "MEMBER", "comments": 3, "first": "2026-10-21", "last": "2026-10-28" } ], "derivation": "substantive support, no open objection (ismaelsadeeq, enirox001)", "model_state": null, "corrections": [], "notes": "Sjors benchmarked making the block template immutable and returning the full block in submitSolution(), identifying an IPC single-thread latency penalty in sv2-tp and recommending deferring immutability until IPC improvements land." }, "dependencies": { "depends_on": [], "enables": [] }, "categories": [ { "name": "ipc", "member": false, "evidence": "Changes what the mining interface exposes and how block templates are synchronized rather than IPC infrastructure itself, which the category explicitly excludes.", "band": "Unranked", "reason_tag": "cleanup", "score": 0.0, "factors": { "bug_severity": 2, "leverage": 0, "performance": 1, "security_stability": 2, "user_value": 1 }, "rationale": "Not an IPC PR because the changes concern mining interface methods and block template synchronization rather than serialization, connection handling, or capnp machinery." }, { "name": "mining", "member": true, "evidence": "Has the Mining label and modifies `src/interfaces/mining.h`, `src/node/block_template_manager.*`, and `src/ipc/capnp/mining.capnp`.", "band": "P2", "reason_tag": "bug fix", "score": 0.7, "factors": { "bug_severity": 2, "leverage": 0, "performance": 1, "security_stability": 2, "user_value": 1 }, "rationale": "Resolves a data race where concurrent IPC worker threads access `CBlockTemplate` during `submitSolution()` while another thread reads from it. Ensuring thread-safe template access and exposing `getTotalFees()` directly improves the stability and completeness of the mining interface external Stratum v2 mining consumers rely on." } ], "confidence": "high", "uncertainties": [], "needs": [] }, "cost_usd": 0.0, "source": { "record": "2026-10-30T01:14:19+00:00", "code": "2026-10-16T01:19:08+00:00", "judgments": 2 } }