914fa6e5a7427dea785ec35d3884cb4a5f9d8b50
13
Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
 dcrubro
|
5eaf0b699c
|
Let a node that is behind adopt the peer's branch, and fix two bugs that only appear once a reorg actually applies
Reported: a node at height N+10 on its own short fork, with the peer at N+500,
could never sync. It located the fork point correctly, pooled the branch, and
then refused it forever. At 90s blocks a node is 960 blocks behind after a day
offline, so this is the normal case, not an edge case.
== Why it could never recover ==
The reorg delay was served by LOCAL chain growth alone:
elapsed = tipHeight - observedTip
That only makes sense for a node whose tip is advancing. A node that is behind
has a frozen tip precisely because it is rejecting the branch, so elapsed stays
0 forever while penalty(5) = 42. Both escape hatches also fail: mining out of it
means extending a fork nobody accepts, and the IBD exemption never fires for a
node that is mining, because mining keeps its tip fresh.
Being 490 blocks behind is being behind, not a reorg contest. Refusing to adopt
protects nothing while the node falls a further 40 blocks behind every hour.
The delay is now satisfiable by EITHER side making progress:
localGrowth = tipHeight - observedTip
branchLead = candidateTip - tipHeight (0 if not ahead)
elapsed = max(localGrowth, branchLead)
A branch already extending `penalty` blocks past our tip has demonstrated
exactly what the delay asks for, and every one of those blocks carries PoW we
validated ourselves. Requiring us to independently produce the same amount is
demanding the same proof twice. Only VALIDATED blocks count -- a peer's
advertised height is not evidence and never reaches this code.
It degrades correctly in both directions: a mining node's tip advances, so an
attacker must outpace it by penalty blocks; a node that is only observing
follows the heaviest chain, which is what an observer should do.
== The window has to keep pulling the branch ==
Every forked delivery reset nextReq back to our own tip, so the window
re-requested the same eight heights forever and the pool never grew past the
window size -- branchLead could not rise even in principle. The backward walk
now runs ONCE to establish linkage, then the window marches forward pooling the
branch, retrying adoption per window-full with a final attempt when it drains.
== sync force ==
Operator override that skips the delay for one sync, for a node whose chain is
known to be the wrong one. Threaded explicitly (Chain_ReplaceBranch gains
bypassPenalty, OrphanPool_AttemptAttachForced) rather than through a global, so
nothing a peer sends can reach it. Linkage, work comparison and atomicity still
apply -- it waives only the waiting, and says so loudly in the log.
== Bug found in testing: PoW is branch-relative ==
A block's epoch seed is the last block of the previous epoch ON ITS OWN BRANCH.
Validating a competing branch's block against OUR epoch seed does not merely
fail to resolve: when the chains diverge before the boundary it resolves to the
WRONG seed and rejects a perfectly valid block. Any fork spanning an epoch
boundary was therefore impossible to assemble -- the branch could not grow past
the boundary block, so branchLead stalled one short of it.
The receive path now does self-contained checks only (Block_HasValidStructure:
merkle, transactions, vote, non-empty). Proof of work moved to
Chain_AddBlockLocked, at the point a block joins the chain, where the branch
context is real -- the rollback has put its ancestors in place by then. That is
where the invariant belongs and it removes a duplicate check rather than adding
one. Needs Chain_DagParamsForHeightLocked, because Chain_AddBlockLocked already
holds chainLock for writing and the lock is not recursive.
Consequence worth knowing: the orphan pool can now hold blocks whose work has
not been verified, bounded by MAX_ORPHAN_BLOCKS (512). Each still had to pass
merkle and full transaction/signature validation, and none can reach the chain
unverified.
This bug also affected plain forward sync across block 350000; it was masked
because appending keeps the boundary block in the chain.
== Bug found in testing: stale DAG accepted as current ==
Block_PowHashHeavy matched on epoch index and size but not the seed. A DAG's
content is a function of (seed, size); the epoch index is a label for it. A
reorg is exactly the event that changes the seed while leaving index and size
untouched, so mid-apply the miner's context still held a DAG built from the
PRE-reorg seed, the guard passed, and a valid block was hashed against the wrong
lanes. g_dagSeed now records what each DAG was generated from and both
Block_EnsureAutolykos2Dag and Block_PowHashHeavy compare it.
== Bug found in testing: double free on the failed-apply path ==
SIGABRT in the allocator: free_tiny_botch -> DynArr_destroy -> Block_Destroy ->
Chain_FreeBlockArray -> Chain_ReplaceBranch.
DynArr_push_back stores the struct BY VALUE, so the chain's element and the
caller's block_t share one transactions pointer. Three places free that array
through the chain's copy -- Chain_ClearBlocks, Chain_RollbackToHeightLocked and
Chain_SaveToFile -- and each NULLs only the chain's side, leaving any caller
wrapper dangling. Whether a caller then had to use free() or Block_Destroy() was
a convention carried in comments at every call site plus a consumed-count passed
into Chain_FreeBlockArray. Chain_ReplaceBranch reset that count to 0 after
rolling back a failed apply, which told the cleanup to Block_Destroy exactly the
blocks whose arrays the rollback had just freed.
Rather than fix the count, the aliasing is now safe by construction:
Chain_AddBlockLocked clears the CALLER's transactions pointer immediately after
the push. Since DynArr_destroy(NULL) is a no-op, free(wrapper) and
Block_Destroy(wrapper) become equivalent and both safe regardless of what later
frees the chain's copy. The consumed-count parameter and both counters are gone
-- the thing that could be got wrong no longer exists -- and all call sites are
unified on Block_Destroy.
Placement is deliberate: immediately after the push, not at the end on success.
The ledger pass can fail with the block already in the chain, returning false to
a caller that destroys its wrapper on failure -- OrphanPool_ExtendTip does
exactly that, a third live instance not yet triggered.
Two follow-ons the refactor forced, both improvements anyway: MineAndAppendBlock
read the coinbase for its log line after the add (hoisted above it), and the
success log printed the caller's block rather than the chain's copy.
== Also ==
The deferral line is rate-limited. The maintenance thread retries pooled
branches once a second and elapsed only changes when something moves, so it
printed an identical line every second -- forever, on a node that is not mining.
It now reports each distinct situation once.
== Verification ==
Synthetic fork, node A 5 deep, node B ~60 ahead, EPOCH_LENGTH=8 so the branch
crosses three epoch boundaries:
branchLead climbs 8 -> 16 -> 28 -> 34, crosses penalty(5)=42
Adopted competing branch of 50 block(s) at fork height 20
sync complete: localHeight=70
Chain OK
Repeated under AddressSanitizer: adopted 47 blocks, 0 ASan errors on both nodes.
This matters because the refactor rewrites the exact cleanup path the SIGABRT
came from, and a double free that no longer aborts would otherwise pass silently.
Unit suites pass, including a new assertion "heavy path refuses a DAG built from
a different seed" -- the direct regression for the stale-DAG bug.
Harness note: each node needs its OWN wallet. With a shared one both pay the
same coinbase address, produce identical merkle roots, and at easy difficulty
mine byte-identical blocks -- the fork test silently became a catch-up test.
== Still untested ==
The restore-after-failed-apply path is no longer naturally reachable now that
the two bugs above are fixed, so it needs deliberate corruption to exercise.
Test B (branch only slightly ahead must still DEFER), test C (sync force), and a
TSan pass over the changed paths are outstanding.
|
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dcrubro
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0e721ca389
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Fix reorg penalty scaling direction and rebuild DAG sizing around a miner-signalled band
Two consensus-parameter bugs, both latent today and both guaranteed to become
live splits later. Neither is a regression; both are cheap to fix now and
expensive to fix after launch.
== 1. The reorg penalty scaled with block time the wrong way ==
FetchScheduler_ComputeReorgPenaltyBlocks had TARGET_BLOCK_TIME in the numerator
and REORG_PENALTY_REF_BLOCK_TIME in the denominator. The penalty is counted in
BLOCKS, so the wall-clock protection it actually buys was
penalty(d) * TARGET_BLOCK_TIME ~ d^2 * T^2 / REF
i.e. quadratic in block time, when the stated intent in constants.h is
wall-clock equivalence to the reference scheme defined at REF_BLOCK_TIME = 150.
At T = 90 the chain got 54*d^2 seconds of protection instead of 150*d^2 --
2.78x weaker than intended -- and any future block-time reduction would have
weakened it further, silently.
Swapping the two makes T cancel out of the wall-clock figure:
penalty(d) = ceil(d^2 * REF / T) -> protection ~ d^2 * REF seconds
Penalty in blocks, depth -> before/after: 4 -> 10/27, 8 -> 39/107,
10 -> 60/167, 50 -> 1500/4167, 100 -> 6000/16667.
Verified by rebuilding at TARGET_BLOCK_TIME = 60: wall-clock protection is now
identical at both block times (2400s, 9600s, 15000s, ...), ratio 1.0000. Under
the old formula 60s blocks would have been 56% weaker.
Still integer-only: the ceiling division and saturation guards are unchanged,
and numeratorScale only moves 90 -> 150 while `raised` stays bounded by
REORG_PENALTY_MAX_DEPTH^2 = 1e6, nowhere near overflow.
This is fork choice, not block validity, so mixed-version nodes converge once
the longer penalty expires and no block ever becomes invalid.
== 2. DAG sizing was a fail-open consensus split waiting on block 350000 ==
Fixed, in rough order of severity:
* FAIL-OPEN PoW. Block_CalculateAutolykos2Hash memset the hash to zero on any
failure, and zero compares below every target -- so a DAG that was missing,
mis-sized or had failed to build made *every* block pass PoW validation
instead of rejecting it. PoW checks now fail closed.
* TWO DIVERGENT IMPLEMENTATIONS of the same rule: CalculateTargetDAGSize in
constants.h (mining) and ComputeEpochDagBytesForHeightFromChain in main.c
(verification). They already disagreed at exactly height == EPOCH_LENGTH,
where the constants.h copy underflowed size_t computing
`Chain_Size - 1 - EPOCH_LENGTH` and returned 0.
* A MEANINGLESS DIFFICULTY COUPLING. difficultyTarget is compact-encoded
[1B exponent][3B coefficient]; subtracting two compact values mixes
exponent and mantissa. The first real retarget yields a delta of 900649,
which times DAG_BASE_GROWTH is ~967 TB, so the result was always clamped
and the "proportional" term degenerated to a binary base+maxUp/base-maxDown
switch. The size also never accumulated -- it was always recomputed from
the constant base -- so the documented 1 GB/epoch growth could not happen.
* A NON-EPOCH-ALIGNED SEED. GetNextDAGSeed returned hash(tip) while the
verifier correctly used hash(block[epochIndex * EPOCH_LENGTH - 1]). The
`chainSize % EPOCH_LENGTH == 0` rebuild guard masked this while running,
but startup called it at an arbitrary height -- so a node restarted
mid-epoch built a DAG from a different seed than one that had run straight
through the boundary, and its blocks were rejected.
* UNSIGNED PROMOTION. `DAG_BASE_GROWTH * difficultyDelta` promoted the signed
delta to unsigned long long and wrapped before being assigned back to
int64_t; the main.c copy cast first, so the two also differed in overflow
behaviour. Both are gone.
* A LEAK on the `targetSize <= 0` path in main.c (both block copies).
* A USE-AFTER-FREE at every epoch boundary: Block_RebuildAutolykos2Dag ran
DagClear -> DagAllocate -> DagGenerate from whichever thread advanced the
tip, freeing ctx->dag.buf while miners read it.
* GetAutolykos2Ctx called DagAllocate without DagGenerate, leaving
dag.len == 0 so every heavy hash failed -- which, combined with the
fail-open above, meant "everything is valid". It also memset 1 GiB that
DagGenerate immediately overwrote.
* TOCTOU / lock reentrancy: CalculateTargetDAGSize called Chain_Size 4x and
Chain_GetBlockCopy 2x, each taking chainLock for reading, making it unsafe
to call from a write-locked section.
--- New sizing rule: default-grow inside a hard band ---
DAG size now follows a recurrence gated by a miner signal in the block header,
clamped to [DAG_MIN_SIZE, DAG_MAX_SIZE]:
brake = (hold + down) * DAG_BRAKE_DEN > EPOCH_LENGTH * DAG_BRAKE_NUM
downQ = down * DAG_DOWN_DEN > EPOCH_LENGTH * DAG_DOWN_NUM
downQ(k) && downQ(k-1) -> size -= DAG_EPOCH_STEP (floored at DAG_MIN_SIZE)
brake -> size unchanged
otherwise -> size += DAG_EPOCH_STEP (capped at DAG_MAX_SIZE)
Growth is the default and there is deliberately NO up-vote: every signal a
miner can express only slows the walk or reverses it. Under stratum-style
pooled mining the pool builds the header and therefore controls its share of
the vote, so the mechanism has to be safe under pool capture -- and it is,
because the lever a pool would want (grow the DAG to price out smaller miners)
does not exist. This is NOT because upward capture would be self-defeating: it
would in fact be profitable, since the fixed block reward redistributes to
whoever survives and difficulty retargets down. The protection is the absence
of the lever. The whole upward trajectory is therefore governance
(DAG_EPOCH_STEP, DAG_MAX_SIZE), not signalling.
Braking keeps the DAG small, which helps old hardware and only costs ASIC
resistance -- bounded by DAG_MIN_SIZE, which is the constant that actually
secures the property. Shrinking needs a supermajority sustained across two
consecutive epochs; that gates the onset only, so miners genuinely being
squeezed get relief every epoch rather than every other one.
Thresholds are cross-multiplied rather than divided, so there is no rounding
for nodes to disagree on, and the denominator is the constant epoch length
rather than blocks-observed, so a partial epoch cannot read as a stronger
signal than it is. No floating point anywhere on this path.
--- Header vote field ---
reserved[0] carries the vote: 0 = grow (default), 1 = hold, 2 = down.
reserved[1..2] must be zero. All three already sat inside the packed, hashed
header, so the vote is committed to by both the canonical hash and the PoW hash
and cannot be altered after mining -- no wire-format or hash-layout change.
0 must mean grow, because the point of this shape is that inaction produces
growth; it also means a miner that knows nothing about the vote contributes to
the intended default rather than silently freezing the schedule.
Rejecting unrecognised vote values and non-zero spare bytes is a new validity
rule. It closes 24 bits of undefined-meaning malleable header space.
--- Validation moves to the light path ---
Autolykos2_DagGenerate fills lane i with exactly what ReadDagLaneFromSeed
recomputes for lane i -- Blake2b(seed || (i/2)_LE64), half i&1 -- so the DAG is
a pure cache and the two hashing paths are bit-for-bit equivalent. Validation
therefore uses the light path: no allocation, correct for any epoch rather than
only whichever one the global DAG happens to hold, and the DAG band becomes a
miner requirement rather than a full-node memory requirement.
Chain_OnTipAdvanced no longer rebuilds the DAG at all. MineBlock builds it on
demand for the height it is working on, so a node that does not mine never
allocates one, generation stays off the tip-advance path, and the buffer is
only ever touched by the miner (the ctx mutex remains as a backstop).
--- API changes ---
+ Chain_DagParamsForHeight(chain, height, &dagBytes, seed) -- single source
of truth for both the size and the epoch seed, backed by a memoised
per-epoch table on blockchain_t. The table is a pure cache of a function of
the headers, extended lazily and dropped whenever anything at or below the
tip changes; it lives on the chain rather than in a global because a
second, header-only chain is built to re-verify historical PoW. Guarded by
a per-chain mutex, always taken after chainLock.
+ Block_EnsureAutolykos2Dag / Block_PowHashHeavy / Block_PowHashLight.
The heavy variant verifies the epoch and size itself, so it can never
answer from a DAG built for another epoch.
+ Block_HasValidProofOfWorkWithParams -- resolve-once form. MineBlock called
Block_HasValidProofOfWork inside its nonce loop, so resolving from the
chain per attempt would have taken chainLock millions of times per block.
+ Block_HasValidVote.
~ Block_HasValidProofOfWork / Block_IsFullyValid now take the chain, because
PoW validity genuinely is chain-relative. blockchain_t gained a struct tag
so block.h can forward-declare it.
- CalculateTargetDAGSize, GetNextDAGSeed, ComputeEpochDagBytesForHeightFromChain,
ComputeEpochSeedForHeightFromChain, Block_CalculateAutolykos2Hash,
Block_RebuildAutolykos2Dag, Autolykos2_LightHash (dead).
- DAG_BASE_GROWTH and the five DAG_MAX_*_SWING_* / DAG_SWING_PERCENT_DEN
macros, all now unreachable.
Also: Block_CalculateAutolykos2Hash truncated the height to uint32 while the
light path takes uint64, so the two would have diverged above block 2^32; the
full width is now passed. Added a `dagvote <grow|hold|down>` REPL command and a
progress line during DAG generation, which is tens of seconds at production
sizes.
static_asserts now enforce DAG_MIN_SIZE <= DAG_BASE_SIZE <= DAG_MAX_SIZE and
32-byte alignment, so a misconfigured band fails the build instead of being
silently clamped.
NOTE: DAG_MIN_SIZE (2 GiB), DAG_BASE_SIZE (2 GiB), DAG_MAX_SIZE (8 GiB) and
DAG_EPOCH_STEP (1 GiB) are economic judgements, not derivations, and since the
vote cannot accelerate growth they are the entire upward story. Sanity-check
them before launch.
== Verification ==
* Penalty: exact table match at d = 4/8/10/50/100/1000, zero within grace,
saturation at MAX_DEPTH, and identical wall-clock protection when rebuilt
at TARGET_BLOCK_TIME = 60.
* DAG recurrence (30 assertions against the real objects): default growth,
legacy all-zero headers read as grow, strict inequality at exactly 1/2 and
exactly 7/8, one qualifying epoch freezes but does not shrink, two
consecutive shrink, sustained shrink repeats, both clamps saturate.
* Epoch seed: constant across an epoch, equal to hash(block[k*EL - 1]),
genesis seed in epoch 0, and resolvable at exactly height == EPOCH_LENGTH.
* Fail-closed: unresolvable params and a zero-byte DAG both reject.
* Heavy/light equivalence across 3 epochs; heavy refuses a DAG built for the
wrong epoch or size.
* Two nodes across 3 epoch boundaries: B reached height 30 purely by
receiving, then mined blocks A accepted; both fullverify Chain OK, zero
rejections.
* Restart mid-epoch: B restarted at height 28 derived epoch 3's seed as
hash(block[23]) -- the boundary block, not the tip -- and kept producing
blocks A accepted. This fails before the change.
* Divergent votes: A voting hold and B voting grow computed identical size
and seed, confirming the tally is chain-derived, not config-derived.
* ThreadSanitizer across epoch rollovers under load: no new races.
|
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dcrubro
|
763aeb648f |
add fee-aware mining, coinbase validation, and reorg-safe orphan handling
Mining: blocks now include mempool txs, select spendable txs by fee, and pay coinbase as base reward + fees in main.c. - Consensus: block validation now enforces coinbase accounting and rejects invalid coinbase placement, including coinbase on amount2, in block.c and transaction.c. - Chain state: rollback now rebuilds currentSupply/currentReward, and block addition preflights spendability before mutating balances in chain.c. - Orphans/reorgs: orphan retry is safer, rollback-triggered sync reattaches orphans immediately, and transient orphan failures no longer drop blocks in orphan_pool.c and main.c. - Networking/mempool: node lifecycle now initializes the mempool, broadcasts can exclude one peer, and mempool snapshotting supports mining selection in net_node.c and txmempool.c. - Ledger simulation: added non-mutating spendable-transaction selection for block assembly in balance_sheet.c. |
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dcrubro
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0fb2615d4c | sync errors | ||
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dcrubro
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3337ac85ab | reorgs, fetch batching (parallel fetch), orphans | ||
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dcrubro
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361ac73e45 | global externs refactor, some tcp methods | ||
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dcrubro
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eb7c29abb1 | pragma packing | ||
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dcrubro
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7aafaa4196 | note | ||
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dcrubro
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b20ba9802e | Full DAG size, epoch scaling etc. | ||
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dcrubro
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b47ff30bc7 | difficulty calculation, move from randomx to autolykos2 | ||
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dcrubro
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c358115af4 | stuff | ||
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dcrubro
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0d7adc39e0 | BigInts, save/load, will make a calculation for block rewards soon | ||
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dcrubro
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57bfe61c13 | Copied TCP impl from other project, basic Block implementation, randomx pow, signing via secp256k1 |