Merge #11281: Avoid permanent cs_main/cs_wallet lock during RescanFromTime

7f81250 Mention that other RPC calls report keys as "imported" while txns are still missing (Jonas Schnelli)
ccd8ef6 Reduce cs_main lock in ReadBlockFromDisk, only read GetBlockPos under the lock (Jonas Schnelli)
bc356b4 Make sure WalletRescanReserver has successfully reserved the rescan (Jonas Schnelli)
dbf8556 Add RAII wallet rescan reserver (Jonas Schnelli)
8d0b610 Avoid pemanent cs_main/cs_wallet lock during wallet rescans (Jonas Schnelli)

Pull request description:

  Right now, we are holding `cs_main`/`cs_wallet` during the whole rescan process (which can take a couple of hours).
  This was probably only done because of laziness and it is an important show-stopper for #11200 (GUI rescan abort).

Tree-SHA512: 0fc3f82d0ee9b2f013e6bacba8d59f7334306660cd676cd64c47bb305c4cb7c7a36219d6a6f76023b74e5fe87f3ab9fc7fd2439e939f71aef653fddb0a1e23b1

src/qt/test/wallettests.cpp

@@ -169,7 +169,9 @@ void TestGUI()
     }
     {
         LOCK(cs_main);
-        wallet.ScanForWalletTransactions(chainActive.Genesis(), nullptr, true);
+        WalletRescanReserver reserver(&wallet);
+        reserver.reserve();
+        wallet.ScanForWalletTransactions(chainActive.Genesis(), nullptr, reserver, true);
     }
     wallet.SetBroadcastTransactions(true);
 

src/validation.cpp

@@ -1121,7 +1121,13 @@ bool ReadBlockFromDisk(CBlock& block, const CDiskBlockPos& pos, const Consensus:
 
 bool ReadBlockFromDisk(CBlock& block, const CBlockIndex* pindex, const Consensus::Params& consensusParams)
 {
-    if (!ReadBlockFromDisk(block, pindex->GetBlockPos(), consensusParams))
+    CDiskBlockPos blockPos;
+    {
+        LOCK(cs_main);
+        blockPos = pindex->GetBlockPos();
+    }
+
+    if (!ReadBlockFromDisk(block, blockPos, consensusParams))
         return false;
     if (block.GetHash() != pindex->GetBlockHash())
         return error("ReadBlockFromDisk(CBlock&, CBlockIndex*): GetHash() doesn't match index for %s at %s",

src/wallet/rpcdump.cpp

@@ -86,7 +86,8 @@ UniValue importprivkey(const JSONRPCRequest& request)
             "1. \"privkey\"          (string, required) The private key (see dumpprivkey)\n"
             "2. \"label\"            (string, optional, default=\"\") An optional label\n"
             "3. rescan               (boolean, optional, default=true) Rescan the wallet for transactions\n"
-            "\nNote: This call can take minutes to complete if rescan is true.\n"
+            "\nNote: This call can take minutes to complete if rescan is true, during that time, other rpc calls\n"
+            "may report that the imported key exists but related transactions are still missing, leading to temporarily incorrect/bogus balances and unspent outputs until rescan completes.\n"
             "\nExamples:\n"
             "\nDump a private key\n"
             + HelpExampleCli("dumpprivkey", "\"myaddress\"") +
@@ -101,6 +102,9 @@ UniValue importprivkey(const JSONRPCRequest& request)
         );
 
 
+    WalletRescanReserver reserver(pwallet);
+    bool fRescan = true;
+    {
         LOCK2(cs_main, pwallet->cs_wallet);
 
         EnsureWalletIsUnlocked(pwallet);
@@ -111,13 +115,16 @@ UniValue importprivkey(const JSONRPCRequest& request)
             strLabel = request.params[1].get_str();
 
         // Whether to perform rescan after import
-    bool fRescan = true;
         if (!request.params[2].isNull())
             fRescan = request.params[2].get_bool();
 
         if (fRescan && fPruneMode)
             throw JSONRPCError(RPC_WALLET_ERROR, "Rescan is disabled in pruned mode");
 
+        if (fRescan && !reserver.reserve()) {
+            throw JSONRPCError(RPC_WALLET_ERROR, "Wallet is currently rescanning. Abort existing rescan or wait.");
+        }
+
         CBitcoinSecret vchSecret;
         bool fGood = vchSecret.SetString(strSecret);
 
@@ -131,7 +138,6 @@ UniValue importprivkey(const JSONRPCRequest& request)
         CKeyID vchAddress = pubkey.GetID();
         {
             pwallet->MarkDirty();
-
             // We don't know which corresponding address will be used; label them all
             for (const auto& dest : GetAllDestinationsForKey(pubkey)) {
                 pwallet->SetAddressBook(dest, strLabel, "receive");
@@ -142,20 +148,19 @@ UniValue importprivkey(const JSONRPCRequest& request)
                 return NullUniValue;
             }
 
+            // whenever a key is imported, we need to scan the whole chain
+            pwallet->UpdateTimeFirstKey(1);
             pwallet->mapKeyMetadata[vchAddress].nCreateTime = 1;
 
             if (!pwallet->AddKeyPubKey(key, pubkey)) {
                 throw JSONRPCError(RPC_WALLET_ERROR, "Error adding key to wallet");
             }
             pwallet->LearnAllRelatedScripts(pubkey);
-
-        // whenever a key is imported, we need to scan the whole chain
-        pwallet->UpdateTimeFirstKey(1);
-
-        if (fRescan) {
-            pwallet->RescanFromTime(TIMESTAMP_MIN, true /* update */);
         }
     }
+    if (fRescan) {
+        pwallet->RescanFromTime(TIMESTAMP_MIN, reserver, true /* update */);
+    }
 
     return NullUniValue;
 }
@@ -237,7 +242,8 @@ UniValue importaddress(const JSONRPCRequest& request)
             "2. \"label\"            (string, optional, default=\"\") An optional label\n"
             "3. rescan               (boolean, optional, default=true) Rescan the wallet for transactions\n"
             "4. p2sh                 (boolean, optional, default=false) Add the P2SH version of the script as well\n"
-            "\nNote: This call can take minutes to complete if rescan is true.\n"
+            "\nNote: This call can take minutes to complete if rescan is true, during that time, other rpc calls\n"
+            "may report that the imported address exists but related transactions are still missing, leading to temporarily incorrect/bogus balances and unspent outputs until rescan completes.\n"
             "If you have the full public key, you should call importpubkey instead of this.\n"
             "\nNote: If you import a non-standard raw script in hex form, outputs sending to it will be treated\n"
             "as change, and not show up in many RPCs.\n"
@@ -263,11 +269,17 @@ UniValue importaddress(const JSONRPCRequest& request)
     if (fRescan && fPruneMode)
         throw JSONRPCError(RPC_WALLET_ERROR, "Rescan is disabled in pruned mode");
 
+    WalletRescanReserver reserver(pwallet);
+    if (fRescan && !reserver.reserve()) {
+        throw JSONRPCError(RPC_WALLET_ERROR, "Wallet is currently rescanning. Abort existing rescan or wait.");
+    }
+
     // Whether to import a p2sh version, too
     bool fP2SH = false;
     if (!request.params[3].isNull())
         fP2SH = request.params[3].get_bool();
 
+    {
         LOCK2(cs_main, pwallet->cs_wallet);
 
         CTxDestination dest = DecodeDestination(request.params[0].get_str());
@@ -282,10 +294,10 @@ UniValue importaddress(const JSONRPCRequest& request)
         } else {
             throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid Bitcoin address or script");
         }
-
+    }
     if (fRescan)
     {
-        pwallet->RescanFromTime(TIMESTAMP_MIN, true /* update */);
+        pwallet->RescanFromTime(TIMESTAMP_MIN, reserver, true /* update */);
         pwallet->ReacceptWalletTransactions();
     }
 
@@ -406,7 +418,8 @@ UniValue importpubkey(const JSONRPCRequest& request)
             "1. \"pubkey\"           (string, required) The hex-encoded public key\n"
             "2. \"label\"            (string, optional, default=\"\") An optional label\n"
             "3. rescan               (boolean, optional, default=true) Rescan the wallet for transactions\n"
-            "\nNote: This call can take minutes to complete if rescan is true.\n"
+            "\nNote: This call can take minutes to complete if rescan is true, during that time, other rpc calls\n"
+            "may report that the imported pubkey exists but related transactions are still missing, leading to temporarily incorrect/bogus balances and unspent outputs until rescan completes.\n"
             "\nExamples:\n"
             "\nImport a public key with rescan\n"
             + HelpExampleCli("importpubkey", "\"mypubkey\"") +
@@ -429,6 +442,11 @@ UniValue importpubkey(const JSONRPCRequest& request)
     if (fRescan && fPruneMode)
         throw JSONRPCError(RPC_WALLET_ERROR, "Rescan is disabled in pruned mode");
 
+    WalletRescanReserver reserver(pwallet);
+    if (fRescan && !reserver.reserve()) {
+        throw JSONRPCError(RPC_WALLET_ERROR, "Wallet is currently rescanning. Abort existing rescan or wait.");
+    }
+
     if (!IsHex(request.params[0].get_str()))
         throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Pubkey must be a hex string");
     std::vector<unsigned char> data(ParseHex(request.params[0].get_str()));
@@ -436,6 +454,7 @@ UniValue importpubkey(const JSONRPCRequest& request)
     if (!pubKey.IsFullyValid())
         throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Pubkey is not a valid public key");
 
+    {
         LOCK2(cs_main, pwallet->cs_wallet);
 
         for (const auto& dest : GetAllDestinationsForKey(pubKey)) {
@@ -443,10 +462,10 @@ UniValue importpubkey(const JSONRPCRequest& request)
         }
         ImportScript(pwallet, GetScriptForRawPubKey(pubKey), strLabel, false);
         pwallet->LearnAllRelatedScripts(pubKey);
-
+    }
     if (fRescan)
     {
-        pwallet->RescanFromTime(TIMESTAMP_MIN, true /* update */);
+        pwallet->RescanFromTime(TIMESTAMP_MIN, reserver, true /* update */);
         pwallet->ReacceptWalletTransactions();
     }
 
@@ -479,18 +498,24 @@ UniValue importwallet(const JSONRPCRequest& request)
     if (fPruneMode)
         throw JSONRPCError(RPC_WALLET_ERROR, "Importing wallets is disabled in pruned mode");
 
+    WalletRescanReserver reserver(pwallet);
+    if (!reserver.reserve()) {
+        throw JSONRPCError(RPC_WALLET_ERROR, "Wallet is currently rescanning. Abort existing rescan or wait.");
+    }
+
+    int64_t nTimeBegin = 0;
+    bool fGood = true;
+    {
         LOCK2(cs_main, pwallet->cs_wallet);
 
         EnsureWalletIsUnlocked(pwallet);
 
         std::ifstream file;
         file.open(request.params[0].get_str().c_str(), std::ios::in | std::ios::ate);
-    if (!file.is_open())
+        if (!file.is_open()) {
             throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot open wallet dump file");
-
-    int64_t nTimeBegin = chainActive.Tip()->GetBlockTime();
-
-    bool fGood = true;
+        }
+        nTimeBegin = chainActive.Tip()->GetBlockTime();
 
         int64_t nFilesize = std::max((int64_t)1, (int64_t)file.tellg());
         file.seekg(0, file.beg);
@@ -563,7 +588,8 @@ UniValue importwallet(const JSONRPCRequest& request)
         file.close();
         pwallet->ShowProgress("", 100); // hide progress dialog in GUI
         pwallet->UpdateTimeFirstKey(nTimeBegin);
-    pwallet->RescanFromTime(nTimeBegin, false /* update */);
+    }
+    pwallet->RescanFromTime(nTimeBegin, reserver, false /* update */);
     pwallet->MarkDirty();
 
     if (!fGood)
@@ -1110,6 +1136,8 @@ UniValue importmulti(const JSONRPCRequest& mainRequest)
             "  {\n"
             "     \"rescan\": <false>,         (boolean, optional, default: true) Stating if should rescan the blockchain after all imports\n"
             "  }\n"
+            "\nNote: This call can take minutes to complete if rescan is true, during that time, other rpc calls\n"
+            "may report that the imported keys, addresses or scripts exists but related transactions are still missing.\n"
             "\nExamples:\n" +
             HelpExampleCli("importmulti", "'[{ \"scriptPubKey\": { \"address\": \"<my address>\" }, \"timestamp\":1455191478 }, "
                                           "{ \"scriptPubKey\": { \"address\": \"<my 2nd address>\" }, \"label\": \"example 2\", \"timestamp\": 1455191480 }]'") +
@@ -1135,18 +1163,26 @@ UniValue importmulti(const JSONRPCRequest& mainRequest)
         }
     }
 
+    WalletRescanReserver reserver(pwallet);
+    if (fRescan && !reserver.reserve()) {
+        throw JSONRPCError(RPC_WALLET_ERROR, "Wallet is currently rescanning. Abort existing rescan or wait.");
+    }
+
+    int64_t now = 0;
+    bool fRunScan = false;
+    int64_t nLowestTimestamp = 0;
+    UniValue response(UniValue::VARR);
+    {
         LOCK2(cs_main, pwallet->cs_wallet);
         EnsureWalletIsUnlocked(pwallet);
 
         // Verify all timestamps are present before importing any keys.
-    const int64_t now = chainActive.Tip() ? chainActive.Tip()->GetMedianTimePast() : 0;
+        now = chainActive.Tip() ? chainActive.Tip()->GetMedianTimePast() : 0;
         for (const UniValue& data : requests.getValues()) {
             GetImportTimestamp(data, now);
         }
 
-    bool fRunScan = false;
         const int64_t minimumTimestamp = 1;
-    int64_t nLowestTimestamp = 0;
 
         if (fRescan && chainActive.Tip()) {
             nLowestTimestamp = chainActive.Tip()->GetBlockTime();
@@ -1154,8 +1190,6 @@ UniValue importmulti(const JSONRPCRequest& mainRequest)
             fRescan = false;
         }
 
-    UniValue response(UniValue::VARR);
-
         for (const UniValue& data : requests.getValues()) {
             const int64_t timestamp = std::max(GetImportTimestamp(data, now), minimumTimestamp);
             const UniValue result = ProcessImport(pwallet, data, timestamp);
@@ -1175,9 +1209,9 @@ UniValue importmulti(const JSONRPCRequest& mainRequest)
                 nLowestTimestamp = timestamp;
             }
         }
-
+    }
     if (fRescan && fRunScan && requests.size()) {
-        int64_t scannedTime = pwallet->RescanFromTime(nLowestTimestamp, true /* update */);
+        int64_t scannedTime = pwallet->RescanFromTime(nLowestTimestamp, reserver, true /* update */);
         pwallet->ReacceptWalletTransactions();
 
         if (scannedTime > nLowestTimestamp) {

src/wallet/rpcwallet.cpp

@@ -3416,10 +3416,19 @@ UniValue rescanblockchain(const JSONRPCRequest& request)
             );
     }
 
-    LOCK2(cs_main, pwallet->cs_wallet);
+    WalletRescanReserver reserver(pwallet);
+    if (!reserver.reserve()) {
+        throw JSONRPCError(RPC_WALLET_ERROR, "Wallet is currently rescanning. Abort existing rescan or wait.");
+    }
 
-    CBlockIndex *pindexStart = chainActive.Genesis();
+    CBlockIndex *pindexStart = nullptr;
     CBlockIndex *pindexStop = nullptr;
+    CBlockIndex *pChainTip = nullptr;
+    {
+        LOCK(cs_main);
+        pindexStart = chainActive.Genesis();
+        pChainTip = chainActive.Tip();
+
         if (!request.params[0].isNull()) {
             pindexStart = chainActive[request.params[0].get_int()];
             if (!pindexStart) {
@@ -3436,10 +3445,12 @@ UniValue rescanblockchain(const JSONRPCRequest& request)
                 throw JSONRPCError(RPC_INVALID_PARAMETER, "stop_height must be greater then start_height");
             }
         }
+    }
 
     // We can't rescan beyond non-pruned blocks, stop and throw an error
     if (fPruneMode) {
-        CBlockIndex *block = pindexStop ? pindexStop : chainActive.Tip();
+        LOCK(cs_main);
+        CBlockIndex *block = pindexStop ? pindexStop : pChainTip;
         while (block && block->nHeight >= pindexStart->nHeight) {
             if (!(block->nStatus & BLOCK_HAVE_DATA)) {
                 throw JSONRPCError(RPC_MISC_ERROR, "Can't rescan beyond pruned data. Use RPC call getblockchaininfo to determine your pruned height.");
@@ -3448,18 +3459,17 @@ UniValue rescanblockchain(const JSONRPCRequest& request)
         }
     }
 
-    CBlockIndex *stopBlock = pwallet->ScanForWalletTransactions(pindexStart, pindexStop, true);
+    CBlockIndex *stopBlock = pwallet->ScanForWalletTransactions(pindexStart, pindexStop, reserver, true);
     if (!stopBlock) {
         if (pwallet->IsAbortingRescan()) {
             throw JSONRPCError(RPC_MISC_ERROR, "Rescan aborted.");
         }
         // if we got a nullptr returned, ScanForWalletTransactions did rescan up to the requested stopindex
-        stopBlock = pindexStop ? pindexStop : chainActive.Tip();
+        stopBlock = pindexStop ? pindexStop : pChainTip;
     }
     else {
         throw JSONRPCError(RPC_MISC_ERROR, "Rescan failed. Potentially corrupted data files.");
     }
-
     UniValue response(UniValue::VOBJ);
     response.pushKV("start_height", pindexStart->nHeight);
     response.pushKV("stop_height", stopBlock->nHeight);

src/wallet/test/wallet_tests.cpp

@@ -384,7 +384,9 @@ BOOST_FIXTURE_TEST_CASE(rescan, TestChain100Setup)
     {
         CWallet wallet;
         AddKey(wallet, coinbaseKey);
-        BOOST_CHECK_EQUAL(nullBlock, wallet.ScanForWalletTransactions(oldTip, nullptr));
+        WalletRescanReserver reserver(&wallet);
+        reserver.reserve();
+        BOOST_CHECK_EQUAL(nullBlock, wallet.ScanForWalletTransactions(oldTip, nullptr, reserver));
         BOOST_CHECK_EQUAL(wallet.GetImmatureBalance(), 100 * COIN);
     }
 
@@ -397,7 +399,9 @@ BOOST_FIXTURE_TEST_CASE(rescan, TestChain100Setup)
     {
         CWallet wallet;
         AddKey(wallet, coinbaseKey);
-        BOOST_CHECK_EQUAL(oldTip, wallet.ScanForWalletTransactions(oldTip, nullptr));
+        WalletRescanReserver reserver(&wallet);
+        reserver.reserve();
+        BOOST_CHECK_EQUAL(oldTip, wallet.ScanForWalletTransactions(oldTip, nullptr, reserver));
         BOOST_CHECK_EQUAL(wallet.GetImmatureBalance(), 50 * COIN);
     }
 
@@ -608,7 +612,9 @@ public:
         bool firstRun;
         wallet->LoadWallet(firstRun);
         AddKey(*wallet, coinbaseKey);
-        wallet->ScanForWalletTransactions(chainActive.Genesis(), nullptr);
+        WalletRescanReserver reserver(wallet.get());
+        reserver.reserve();
+        wallet->ScanForWalletTransactions(chainActive.Genesis(), nullptr, reserver);
     }
 
     ~ListCoinsTestingSetup()

src/wallet/wallet.cpp

@@ -1612,19 +1612,20 @@ void CWalletTx::GetAmounts(std::list<COutputEntry>& listReceived,
  * @return Earliest timestamp that could be successfully scanned from. Timestamp
  * returned will be higher than startTime if relevant blocks could not be read.
  */
-int64_t CWallet::RescanFromTime(int64_t startTime, bool update)
+int64_t CWallet::RescanFromTime(int64_t startTime, const WalletRescanReserver& reserver, bool update)
 {
-    AssertLockHeld(cs_main);
-    AssertLockHeld(cs_wallet);
-
     // Find starting block. May be null if nCreateTime is greater than the
     // highest blockchain timestamp, in which case there is nothing that needs
     // to be scanned.
-    CBlockIndex* const startBlock = chainActive.FindEarliestAtLeast(startTime - TIMESTAMP_WINDOW);
+    CBlockIndex* startBlock = nullptr;
+    {
+        LOCK(cs_main);
+        startBlock = chainActive.FindEarliestAtLeast(startTime - TIMESTAMP_WINDOW);
         LogPrintf("%s: Rescanning last %i blocks\n", __func__, startBlock ? chainActive.Height() - startBlock->nHeight + 1 : 0);
+    }
 
     if (startBlock) {
-        const CBlockIndex* const failedBlock = ScanForWalletTransactions(startBlock, nullptr, update);
+        const CBlockIndex* const failedBlock = ScanForWalletTransactions(startBlock, nullptr, reserver, update);
         if (failedBlock) {
             return failedBlock->GetBlockTimeMax() + TIMESTAMP_WINDOW + 1;
         }
@@ -1643,12 +1644,17 @@ int64_t CWallet::RescanFromTime(int64_t startTime, bool update)
  *
  * If pindexStop is not a nullptr, the scan will stop at the block-index
  * defined by pindexStop
+ *
+ * Caller needs to make sure pindexStop (and the optional pindexStart) are on
+ * the main chain after to the addition of any new keys you want to detect
+ * transactions for.
  */
-CBlockIndex* CWallet::ScanForWalletTransactions(CBlockIndex* pindexStart, CBlockIndex* pindexStop, bool fUpdate)
+CBlockIndex* CWallet::ScanForWalletTransactions(CBlockIndex* pindexStart, CBlockIndex* pindexStop, const WalletRescanReserver &reserver, bool fUpdate)
 {
     int64_t nNow = GetTime();
     const CChainParams& chainParams = Params();
 
+    assert(reserver.isReserved());
     if (pindexStop) {
         assert(pindexStop->nHeight >= pindexStart->nHeight);
     }
@@ -1656,24 +1662,42 @@ CBlockIndex* CWallet::ScanForWalletTransactions(CBlockIndex* pindexStart, CBlock
     CBlockIndex* pindex = pindexStart;
     CBlockIndex* ret = nullptr;
     {
-        LOCK2(cs_main, cs_wallet);
         fAbortRescan = false;
-        fScanningWallet = true;
-
         ShowProgress(_("Rescanning..."), 0); // show rescan progress in GUI as dialog or on splashscreen, if -rescan on startup
-        double dProgressStart = GuessVerificationProgress(chainParams.TxData(), pindex);
-        double dProgressTip = GuessVerificationProgress(chainParams.TxData(), chainActive.Tip());
+        CBlockIndex* tip = nullptr;
+        double dProgressStart;
+        double dProgressTip;
+        {
+            LOCK(cs_main);
+            tip = chainActive.Tip();
+            dProgressStart = GuessVerificationProgress(chainParams.TxData(), pindex);
+            dProgressTip = GuessVerificationProgress(chainParams.TxData(), tip);
+        }
         while (pindex && !fAbortRescan)
         {
-            if (pindex->nHeight % 100 == 0 && dProgressTip - dProgressStart > 0.0)
-                ShowProgress(_("Rescanning..."), std::max(1, std::min(99, (int)((GuessVerificationProgress(chainParams.TxData(), pindex) - dProgressStart) / (dProgressTip - dProgressStart) * 100))));
+            if (pindex->nHeight % 100 == 0 && dProgressTip - dProgressStart > 0.0) {
+                double gvp = 0;
+                {
+                    LOCK(cs_main);
+                    gvp = GuessVerificationProgress(chainParams.TxData(), pindex);
+                }
+                ShowProgress(_("Rescanning..."), std::max(1, std::min(99, (int)((gvp - dProgressStart) / (dProgressTip - dProgressStart) * 100))));
+            }
             if (GetTime() >= nNow + 60) {
                 nNow = GetTime();
+                LOCK(cs_main);
                 LogPrintf("Still rescanning. At block %d. Progress=%f\n", pindex->nHeight, GuessVerificationProgress(chainParams.TxData(), pindex));
             }
 
             CBlock block;
             if (ReadBlockFromDisk(block, pindex, Params().GetConsensus())) {
+                LOCK2(cs_main, cs_wallet);
+                if (pindex && !chainActive.Contains(pindex)) {
+                    // Abort scan if current block is no longer active, to prevent
+                    // marking transactions as coming from the wrong block.
+                    ret = pindex;
+                    break;
+                }
                 for (size_t posInBlock = 0; posInBlock < block.vtx.size(); ++posInBlock) {
                     AddToWalletIfInvolvingMe(block.vtx[posInBlock], pindex, posInBlock, fUpdate);
                 }
@@ -1683,14 +1707,20 @@ CBlockIndex* CWallet::ScanForWalletTransactions(CBlockIndex* pindexStart, CBlock
             if (pindex == pindexStop) {
                 break;
             }
+            {
+                LOCK(cs_main);
                 pindex = chainActive.Next(pindex);
+                if (tip != chainActive.Tip()) {
+                    tip = chainActive.Tip();
+                    // in case the tip has changed, update progress max
+                    dProgressTip = GuessVerificationProgress(chainParams.TxData(), tip);
+                }
+            }
         }
         if (pindex && fAbortRescan) {
             LogPrintf("Rescan aborted at block %d. Progress=%f\n", pindex->nHeight, GuessVerificationProgress(chainParams.TxData(), pindex));
         }
         ShowProgress(_("Rescanning..."), 100); // hide progress dialog in GUI
-
-        fScanningWallet = false;
     }
     return ret;
 }
@@ -4001,7 +4031,14 @@ CWallet* CWallet::CreateWalletFromFile(const std::string walletFile)
         }
 
         nStart = GetTimeMillis();
-        walletInstance->ScanForWalletTransactions(pindexRescan, nullptr, true);
+        {
+            WalletRescanReserver reserver(walletInstance);
+            if (!reserver.reserve()) {
+                InitError(_("Failed to rescan the wallet during initialization"));
+                return nullptr;
+            }
+            walletInstance->ScanForWalletTransactions(pindexRescan, nullptr, reserver, true);
+        }
         LogPrintf(" rescan      %15dms\n", GetTimeMillis() - nStart);
         walletInstance->SetBestChain(chainActive.GetLocator());
         walletInstance->dbw->IncrementUpdateCounter();

src/wallet/wallet.h

@@ -659,6 +659,7 @@ private:
 };
 
 
+class WalletRescanReserver; //forward declarations for ScanForWalletTransactions/RescanFromTime
 /** 
  * A CWallet is an extension of a keystore, which also maintains a set of transactions and balances,
  * and provides the ability to create new transactions.
@@ -668,7 +669,10 @@ class CWallet final : public CCryptoKeyStore, public CValidationInterface
 private:
     static std::atomic<bool> fFlushScheduled;
     std::atomic<bool> fAbortRescan;
-    std::atomic<bool> fScanningWallet;
+    std::atomic<bool> fScanningWallet; //controlled by WalletRescanReserver
+    std::mutex mutexScanning;
+    friend class WalletRescanReserver;
+
 
     /**
      * Select a set of coins such that nValueRet >= nTargetValue and at least
@@ -945,8 +949,8 @@ public:
     void BlockConnected(const std::shared_ptr<const CBlock>& pblock, const CBlockIndex *pindex, const std::vector<CTransactionRef>& vtxConflicted) override;
     void BlockDisconnected(const std::shared_ptr<const CBlock>& pblock) override;
     bool AddToWalletIfInvolvingMe(const CTransactionRef& tx, const CBlockIndex* pIndex, int posInBlock, bool fUpdate);
-    int64_t RescanFromTime(int64_t startTime, bool update);
-    CBlockIndex* ScanForWalletTransactions(CBlockIndex* pindexStart, CBlockIndex* pindexStop, bool fUpdate = false);
+    int64_t RescanFromTime(int64_t startTime, const WalletRescanReserver& reserver, bool update);
+    CBlockIndex* ScanForWalletTransactions(CBlockIndex* pindexStart, CBlockIndex* pindexStop, const WalletRescanReserver& reserver, bool fUpdate = false);
     void TransactionRemovedFromMempool(const CTransactionRef &ptx) override;
     void ReacceptWalletTransactions();
     void ResendWalletTransactions(int64_t nBestBlockTime, CConnman* connman) override;
@@ -1263,4 +1267,39 @@ CTxDestination GetDestinationForKey(const CPubKey& key, OutputType);
 /** Get all destinations (potentially) supported by the wallet for the given key. */
 std::vector<CTxDestination> GetAllDestinationsForKey(const CPubKey& key);
 
+/** RAII object to check and reserve a wallet rescan */
+class WalletRescanReserver
+{
+private:
+    CWalletRef m_wallet;
+    bool m_could_reserve;
+public:
+    explicit WalletRescanReserver(CWalletRef w) : m_wallet(w), m_could_reserve(false) {}
+
+    bool reserve()
+    {
+        assert(!m_could_reserve);
+        std::lock_guard<std::mutex> lock(m_wallet->mutexScanning);
+        if (m_wallet->fScanningWallet) {
+            return false;
+        }
+        m_wallet->fScanningWallet = true;
+        m_could_reserve = true;
+        return true;
+    }
+
+    bool isReserved() const
+    {
+        return (m_could_reserve && m_wallet->fScanningWallet);
+    }
+
+    ~WalletRescanReserver()
+    {
+        std::lock_guard<std::mutex> lock(m_wallet->mutexScanning);
+        if (m_could_reserve) {
+            m_wallet->fScanningWallet = false;
+        }
+    }
+};
+
 #endif // BITCOIN_WALLET_WALLET_H