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

7 files changed, 349 insertions, 215 deletions

diff --git a/src/qt/test/wallettests.cpp b/src/qt/test/wallettests.cpp
index a270e5de59..cd49292138 100644
--- a/src/qt/test/wallettests.cpp
+++ b/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);
 
diff --git a/src/validation.cpp b/src/validation.cpp
index 14d60bb269..8cee0dfac3 100644
--- a/src/validation.cpp
+++ b/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",
diff --git a/src/wallet/rpcdump.cpp b/src/wallet/rpcdump.cpp
index 645e776b68..0b021f9fe0 100644
--- a/src/wallet/rpcdump.cpp
+++ b/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\"") +
@@ -101,61 +102,65 @@ UniValue importprivkey(const JSONRPCRequest& request)
         );
 
 
-    LOCK2(cs_main, pwallet->cs_wallet);
-
-    EnsureWalletIsUnlocked(pwallet);
-
-    std::string strSecret = request.params[0].get_str();
-    std::string strLabel = "";
-    if (!request.params[1].isNull())
-        strLabel = request.params[1].get_str();
-
-    // Whether to perform rescan after import
+    WalletRescanReserver reserver(pwallet);
     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");
+    {
+        LOCK2(cs_main, pwallet->cs_wallet);
 
-    CBitcoinSecret vchSecret;
-    bool fGood = vchSecret.SetString(strSecret);
+        EnsureWalletIsUnlocked(pwallet);
 
-    if (!fGood) throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid private key encoding");
+        std::string strSecret = request.params[0].get_str();
+        std::string strLabel = "";
+        if (!request.params[1].isNull())
+            strLabel = request.params[1].get_str();
 
-    CKey key = vchSecret.GetKey();
-    if (!key.IsValid()) throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Private key outside allowed range");
+        // Whether to perform rescan after import
+        if (!request.params[2].isNull())
+            fRescan = request.params[2].get_bool();
 
-    CPubKey pubkey = key.GetPubKey();
-    assert(key.VerifyPubKey(pubkey));
-    CKeyID vchAddress = pubkey.GetID();
-    {
-        pwallet->MarkDirty();
+        if (fRescan && fPruneMode)
+            throw JSONRPCError(RPC_WALLET_ERROR, "Rescan is disabled in pruned mode");
 
-        // We don't know which corresponding address will be used; label them all
-        for (const auto& dest : GetAllDestinationsForKey(pubkey)) {
-            pwallet->SetAddressBook(dest, strLabel, "receive");
+        if (fRescan && !reserver.reserve()) {
+            throw JSONRPCError(RPC_WALLET_ERROR, "Wallet is currently rescanning. Abort existing rescan or wait.");
         }
 
-        // Don't throw error in case a key is already there
-        if (pwallet->HaveKey(vchAddress)) {
-            return NullUniValue;
-        }
+        CBitcoinSecret vchSecret;
+        bool fGood = vchSecret.SetString(strSecret);
 
-        pwallet->mapKeyMetadata[vchAddress].nCreateTime = 1;
+        if (!fGood) throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid private key encoding");
 
-        if (!pwallet->AddKeyPubKey(key, pubkey)) {
-            throw JSONRPCError(RPC_WALLET_ERROR, "Error adding key to wallet");
-        }
-        pwallet->LearnAllRelatedScripts(pubkey);
+        CKey key = vchSecret.GetKey();
+        if (!key.IsValid()) throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Private key outside allowed range");
 
-        // whenever a key is imported, we need to scan the whole chain
-        pwallet->UpdateTimeFirstKey(1);
+        CPubKey pubkey = key.GetPubKey();
+        assert(key.VerifyPubKey(pubkey));
+        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");
+            }
 
-        if (fRescan) {
-            pwallet->RescanFromTime(TIMESTAMP_MIN, true /* update */);
+            // Don't throw error in case a key is already there
+            if (pwallet->HaveKey(vchAddress)) {
+                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);
         }
     }
+    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"
@@ -263,29 +269,35 @@ 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);
+    {
+        LOCK2(cs_main, pwallet->cs_wallet);
 
-    CTxDestination dest = DecodeDestination(request.params[0].get_str());
-    if (IsValidDestination(dest)) {
-        if (fP2SH) {
-            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Cannot use the p2sh flag with an address - use a script instead");
+        CTxDestination dest = DecodeDestination(request.params[0].get_str());
+        if (IsValidDestination(dest)) {
+            if (fP2SH) {
+                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Cannot use the p2sh flag with an address - use a script instead");
+            }
+            ImportAddress(pwallet, dest, strLabel);
+        } else if (IsHex(request.params[0].get_str())) {
+            std::vector<unsigned char> data(ParseHex(request.params[0].get_str()));
+            ImportScript(pwallet, CScript(data.begin(), data.end()), strLabel, fP2SH);
+        } else {
+            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid Bitcoin address or script");
         }
-        ImportAddress(pwallet, dest, strLabel);
-    } else if (IsHex(request.params[0].get_str())) {
-        std::vector<unsigned char> data(ParseHex(request.params[0].get_str()));
-        ImportScript(pwallet, CScript(data.begin(), data.end()), strLabel, fP2SH);
-    } 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()));
@@ -436,17 +454,18 @@ 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);
+    {
+        LOCK2(cs_main, pwallet->cs_wallet);
 
-    for (const auto& dest : GetAllDestinationsForKey(pubKey)) {
-        ImportAddress(pwallet, dest, strLabel);
+        for (const auto& dest : GetAllDestinationsForKey(pubKey)) {
+            ImportAddress(pwallet, dest, strLabel);
+        }
+        ImportScript(pwallet, GetScriptForRawPubKey(pubKey), strLabel, false);
+        pwallet->LearnAllRelatedScripts(pubKey);
     }
-    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();
     }
 
@@ -479,91 +498,98 @@ UniValue importwallet(const JSONRPCRequest& request)
     if (fPruneMode)
         throw JSONRPCError(RPC_WALLET_ERROR, "Importing wallets is disabled in pruned mode");
 
-    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.");
+    }
 
-    EnsureWalletIsUnlocked(pwallet);
+    int64_t nTimeBegin = 0;
+    bool fGood = true;
+    {
+        LOCK2(cs_main, pwallet->cs_wallet);
 
-    std::ifstream file;
-    file.open(request.params[0].get_str().c_str(), std::ios::in | std::ios::ate);
-    if (!file.is_open())
-        throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot open wallet dump file");
+        EnsureWalletIsUnlocked(pwallet);
 
-    int64_t nTimeBegin = chainActive.Tip()->GetBlockTime();
+        std::ifstream file;
+        file.open(request.params[0].get_str().c_str(), std::ios::in | std::ios::ate);
+        if (!file.is_open()) {
+            throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot open wallet dump file");
+        }
+        nTimeBegin = chainActive.Tip()->GetBlockTime();
 
-    bool fGood = true;
+        int64_t nFilesize = std::max((int64_t)1, (int64_t)file.tellg());
+        file.seekg(0, file.beg);
 
-    int64_t nFilesize = std::max((int64_t)1, (int64_t)file.tellg());
-    file.seekg(0, file.beg);
-
-    pwallet->ShowProgress(_("Importing..."), 0); // show progress dialog in GUI
-    while (file.good()) {
-        pwallet->ShowProgress("", std::max(1, std::min(99, (int)(((double)file.tellg() / (double)nFilesize) * 100))));
-        std::string line;
-        std::getline(file, line);
-        if (line.empty() || line[0] == '#')
-            continue;
-
-        std::vector<std::string> vstr;
-        boost::split(vstr, line, boost::is_any_of(" "));
-        if (vstr.size() < 2)
-            continue;
-        CBitcoinSecret vchSecret;
-        if (vchSecret.SetString(vstr[0])) {
-            CKey key = vchSecret.GetKey();
-            CPubKey pubkey = key.GetPubKey();
-            assert(key.VerifyPubKey(pubkey));
-            CKeyID keyid = pubkey.GetID();
-            if (pwallet->HaveKey(keyid)) {
-                LogPrintf("Skipping import of %s (key already present)\n", EncodeDestination(keyid));
+        pwallet->ShowProgress(_("Importing..."), 0); // show progress dialog in GUI
+        while (file.good()) {
+            pwallet->ShowProgress("", std::max(1, std::min(99, (int)(((double)file.tellg() / (double)nFilesize) * 100))));
+            std::string line;
+            std::getline(file, line);
+            if (line.empty() || line[0] == '#')
                 continue;
-            }
-            int64_t nTime = DecodeDumpTime(vstr[1]);
-            std::string strLabel;
-            bool fLabel = true;
-            for (unsigned int nStr = 2; nStr < vstr.size(); nStr++) {
-                if (boost::algorithm::starts_with(vstr[nStr], "#"))
-                    break;
-                if (vstr[nStr] == "change=1")
-                    fLabel = false;
-                if (vstr[nStr] == "reserve=1")
-                    fLabel = false;
-                if (boost::algorithm::starts_with(vstr[nStr], "label=")) {
-                    strLabel = DecodeDumpString(vstr[nStr].substr(6));
-                    fLabel = true;
-                }
-            }
-            LogPrintf("Importing %s...\n", EncodeDestination(keyid));
-            if (!pwallet->AddKeyPubKey(key, pubkey)) {
-                fGood = false;
+
+            std::vector<std::string> vstr;
+            boost::split(vstr, line, boost::is_any_of(" "));
+            if (vstr.size() < 2)
                 continue;
+            CBitcoinSecret vchSecret;
+            if (vchSecret.SetString(vstr[0])) {
+                CKey key = vchSecret.GetKey();
+                CPubKey pubkey = key.GetPubKey();
+                assert(key.VerifyPubKey(pubkey));
+                CKeyID keyid = pubkey.GetID();
+                if (pwallet->HaveKey(keyid)) {
+                    LogPrintf("Skipping import of %s (key already present)\n", EncodeDestination(keyid));
+                    continue;
+                }
+                int64_t nTime = DecodeDumpTime(vstr[1]);
+                std::string strLabel;
+                bool fLabel = true;
+                for (unsigned int nStr = 2; nStr < vstr.size(); nStr++) {
+                    if (boost::algorithm::starts_with(vstr[nStr], "#"))
+                        break;
+                    if (vstr[nStr] == "change=1")
+                        fLabel = false;
+                    if (vstr[nStr] == "reserve=1")
+                        fLabel = false;
+                    if (boost::algorithm::starts_with(vstr[nStr], "label=")) {
+                        strLabel = DecodeDumpString(vstr[nStr].substr(6));
+                        fLabel = true;
+                    }
+                }
+                LogPrintf("Importing %s...\n", EncodeDestination(keyid));
+                if (!pwallet->AddKeyPubKey(key, pubkey)) {
+                    fGood = false;
+                    continue;
+                }
+                pwallet->mapKeyMetadata[keyid].nCreateTime = nTime;
+                if (fLabel)
+                    pwallet->SetAddressBook(keyid, strLabel, "receive");
+                nTimeBegin = std::min(nTimeBegin, nTime);
+            } else if(IsHex(vstr[0])) {
+               std::vector<unsigned char> vData(ParseHex(vstr[0]));
+               CScript script = CScript(vData.begin(), vData.end());
+               if (pwallet->HaveCScript(script)) {
+                   LogPrintf("Skipping import of %s (script already present)\n", vstr[0]);
+                   continue;
+               }
+               if(!pwallet->AddCScript(script)) {
+                   LogPrintf("Error importing script %s\n", vstr[0]);
+                   fGood = false;
+                   continue;
+               }
+               int64_t birth_time = DecodeDumpTime(vstr[1]);
+               if (birth_time > 0) {
+                   pwallet->m_script_metadata[CScriptID(script)].nCreateTime = birth_time;
+                   nTimeBegin = std::min(nTimeBegin, birth_time);
+               }
             }
-            pwallet->mapKeyMetadata[keyid].nCreateTime = nTime;
-            if (fLabel)
-                pwallet->SetAddressBook(keyid, strLabel, "receive");
-            nTimeBegin = std::min(nTimeBegin, nTime);
-        } else if(IsHex(vstr[0])) {
-           std::vector<unsigned char> vData(ParseHex(vstr[0]));
-           CScript script = CScript(vData.begin(), vData.end());
-           if (pwallet->HaveCScript(script)) {
-               LogPrintf("Skipping import of %s (script already present)\n", vstr[0]);
-               continue;
-           }
-           if(!pwallet->AddCScript(script)) {
-               LogPrintf("Error importing script %s\n", vstr[0]);
-               fGood = false;
-               continue;
-           }
-           int64_t birth_time = DecodeDumpTime(vstr[1]);
-           if (birth_time > 0) {
-               pwallet->m_script_metadata[CScriptID(script)].nCreateTime = birth_time;
-               nTimeBegin = std::min(nTimeBegin, birth_time);
-           }
         }
+        file.close();
+        pwallet->ShowProgress("", 100); // hide progress dialog in GUI
+        pwallet->UpdateTimeFirstKey(nTimeBegin);
     }
-    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)
@@ -685,7 +711,7 @@ UniValue dumpwallet(const JSONRPCRequest& request)
     file << strprintf("#   mined on %s\n", EncodeDumpTime(chainActive.Tip()->GetBlockTime()));
     file << "\n";
 
-    // add the base58check encoded extended master if the wallet uses HD 
+    // add the base58check encoded extended master if the wallet uses HD
     CKeyID masterKeyID = pwallet->GetHDChain().masterKeyID;
     if (!masterKeyID.IsNull())
     {
@@ -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 }]'") +
@@ -1135,49 +1163,55 @@ UniValue importmulti(const JSONRPCRequest& mainRequest)
         }
     }
 
-    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;
-    for (const UniValue& data : requests.getValues()) {
-        GetImportTimestamp(data, now);
+    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;
-    const int64_t minimumTimestamp = 1;
     int64_t nLowestTimestamp = 0;
-
-    if (fRescan && chainActive.Tip()) {
-        nLowestTimestamp = chainActive.Tip()->GetBlockTime();
-    } else {
-        fRescan = false;
-    }
-
     UniValue response(UniValue::VARR);
+    {
+        LOCK2(cs_main, pwallet->cs_wallet);
+        EnsureWalletIsUnlocked(pwallet);
 
-    for (const UniValue& data : requests.getValues()) {
-        const int64_t timestamp = std::max(GetImportTimestamp(data, now), minimumTimestamp);
-        const UniValue result = ProcessImport(pwallet, data, timestamp);
-        response.push_back(result);
-
-        if (!fRescan) {
-            continue;
+        // Verify all timestamps are present before importing any keys.
+        now = chainActive.Tip() ? chainActive.Tip()->GetMedianTimePast() : 0;
+        for (const UniValue& data : requests.getValues()) {
+            GetImportTimestamp(data, now);
         }
 
-        // If at least one request was successful then allow rescan.
-        if (result["success"].get_bool()) {
-            fRunScan = true;
+        const int64_t minimumTimestamp = 1;
+
+        if (fRescan && chainActive.Tip()) {
+            nLowestTimestamp = chainActive.Tip()->GetBlockTime();
+        } else {
+            fRescan = false;
         }
 
-        // Get the lowest timestamp.
-        if (timestamp < nLowestTimestamp) {
-            nLowestTimestamp = timestamp;
+        for (const UniValue& data : requests.getValues()) {
+            const int64_t timestamp = std::max(GetImportTimestamp(data, now), minimumTimestamp);
+            const UniValue result = ProcessImport(pwallet, data, timestamp);
+            response.push_back(result);
+
+            if (!fRescan) {
+                continue;
+            }
+
+            // If at least one request was successful then allow rescan.
+            if (result["success"].get_bool()) {
+                fRunScan = true;
+            }
+
+            // Get the lowest timestamp.
+            if (timestamp < nLowestTimestamp) {
+                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) {
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index ad0ebcce22..7770b41e56 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -3416,30 +3416,41 @@ 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;
-    if (!request.params[0].isNull()) {
-        pindexStart = chainActive[request.params[0].get_int()];
-        if (!pindexStart) {
-            throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid start_height");
-        }
-    }
+    CBlockIndex *pChainTip = nullptr;
+    {
+        LOCK(cs_main);
+        pindexStart = chainActive.Genesis();
+        pChainTip = chainActive.Tip();
 
-    if (!request.params[1].isNull()) {
-        pindexStop = chainActive[request.params[1].get_int()];
-        if (!pindexStop) {
-            throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid stop_height");
+        if (!request.params[0].isNull()) {
+            pindexStart = chainActive[request.params[0].get_int()];
+            if (!pindexStart) {
+                throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid start_height");
+            }
         }
-        else if (pindexStop->nHeight < pindexStart->nHeight) {
-            throw JSONRPCError(RPC_INVALID_PARAMETER, "stop_height must be greater then start_height");
+
+        if (!request.params[1].isNull()) {
+            pindexStop = chainActive[request.params[1].get_int()];
+            if (!pindexStop) {
+                throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid stop_height");
+            }
+            else if (pindexStop->nHeight < pindexStart->nHeight) {
+                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);
diff --git a/src/wallet/test/wallet_tests.cpp b/src/wallet/test/wallet_tests.cpp
index 7b3c283f37..7e0881afd7 100644
--- a/src/wallet/test/wallet_tests.cpp
+++ b/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()
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index da721ea008..dd9bc64728 100644
--- a/src/wallet/wallet.cpp
+++ b/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);
-    LogPrintf("%s: Rescanning last %i blocks\n", __func__, startBlock ? chainActive.Height() - startBlock->nHeight + 1 : 0);
+    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;
             }
-            pindex = chainActive.Next(pindex);
+            {
+                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();
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index 8acbade65c..354f524821 100644
--- a/src/wallet/wallet.h
+++ b/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