fix: Guard Coro::resume() against completed coroutines (#6608)

Signed-off-by: Pratik Mankawde <3397372+pratikmankawde@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

include/xrpl/core/Coro.ipp

@@ -70,14 +70,24 @@ JobQueue::Coro::resume()
         running_ = true;
     }
     {
-        std::lock_guard lock(jq_.m_mutex);
+        std::lock_guard lk(jq_.m_mutex);
         --jq_.nSuspend_;
     }
     auto saved = detail::getLocalValues().release();
     detail::getLocalValues().reset(&lvs_);
     std::lock_guard lock(mutex_);
-    XRPL_ASSERT(static_cast<bool>(coro_), "xrpl::JobQueue::Coro::resume : is runnable");
-    coro_();
+    // A late resume() can arrive after the coroutine has already completed.
+    // This is an expected (if rare) outcome of the race condition documented
+    // in JobQueue.h:354-377 where post() schedules a resume job before the
+    // coroutine yields — the mutex serializes access, but by the time this
+    // resume() acquires the lock the coroutine may have already run to
+    // completion. Calling operator() on a completed boost::coroutine2 is
+    // undefined behavior, so we must check and skip invoking the coroutine
+    // body if it has already completed.
+    if (coro_)
+    {
+        coro_();
+    }
     detail::getLocalValues().release();
     detail::getLocalValues().reset(saved);
     std::lock_guard lk(mutex_run_);

include/xrpl/core/JobQueue.h

@@ -99,8 +99,8 @@ public:
             Effects:
                The coroutine continues execution from where it last left off
                  using this same thread.
-            Undefined behavior if called after the coroutine has completed
-              with a return (as opposed to a yield()).
+               If the coroutine has already completed, returns immediately
+                 (handles the documented post-before-yield race condition).
             Undefined behavior if resume() or post() called consecutively
               without a corresponding yield.
         */
@@ -357,8 +357,10 @@ private:
     If the post() job were to be executed before yield(), undefined behavior
     would occur. The lock ensures that coro_ is not called again until we exit
     the coroutine. At which point a scheduled resume() job waiting on the lock
-    would gain entry, harmlessly call coro_ and immediately return as we have
-    already completed the coroutine.
+    would gain entry. resume() checks if the coroutine has already completed
+    (coro_ converts to false) and, if so, skips invoking operator() since
+    calling operator() on a completed boost::coroutine2 pull_type is undefined
+    behavior.
 
     The race condition occurs as follows:
 

include/xrpl/tx/invariants/InvariantCheck.h

@@ -7,6 +7,7 @@
 #include <xrpl/protocol/TER.h>
 #include <xrpl/tx/invariants/AMMInvariant.h>
 #include <xrpl/tx/invariants/FreezeInvariant.h>
+#include <xrpl/tx/invariants/LoanBrokerInvariant.h>
 #include <xrpl/tx/invariants/LoanInvariant.h>
 #include <xrpl/tx/invariants/MPTInvariant.h>
 #include <xrpl/tx/invariants/NFTInvariant.h>

include/xrpl/tx/invariants/LoanBrokerInvariant.h

@@ -0,0 +1,55 @@
+#pragma once
+
+#include <xrpl/basics/base_uint.h>
+#include <xrpl/beast/utility/Journal.h>
+#include <xrpl/ledger/ReadView.h>
+#include <xrpl/protocol/STTx.h>
+#include <xrpl/protocol/TER.h>
+
+#include <map>
+#include <vector>
+
+namespace xrpl {
+
+/**
+ * @brief Invariants: Loan brokers are internally consistent
+ *
+ * 1. If `LoanBroker.OwnerCount = 0` the `DirectoryNode` will have at most one
+ *    node (the root), which will only hold entries for `RippleState` or
+ * `MPToken` objects.
+ *
+ */
+class ValidLoanBroker
+{
+    // Not all of these elements will necessarily be populated. Remaining items
+    // will be looked up as needed.
+    struct BrokerInfo
+    {
+        SLE::const_pointer brokerBefore = nullptr;
+        // After is used for most of the checks, except
+        // those that check changed values.
+        SLE::const_pointer brokerAfter = nullptr;
+    };
+    // Collect all the LoanBrokers found directly or indirectly through
+    // pseudo-accounts. Key is the brokerID / index. It will be used to find the
+    // LoanBroker object if brokerBefore and brokerAfter are nullptr
+    std::map<uint256, BrokerInfo> brokers_;
+    // Collect all the modified trust lines. Their high and low accounts will be
+    // loaded to look for LoanBroker pseudo-accounts.
+    std::vector<SLE::const_pointer> lines_;
+    // Collect all the modified MPTokens. Their accounts will be loaded to look
+    // for LoanBroker pseudo-accounts.
+    std::vector<SLE::const_pointer> mpts_;
+
+    static bool
+    goodZeroDirectory(ReadView const& view, SLE::const_ref dir, beast::Journal const& j);
+
+public:
+    void
+    visitEntry(bool, std::shared_ptr<SLE const> const&, std::shared_ptr<SLE const> const&);
+
+    bool
+    finalize(STTx const&, TER const, XRPAmount const, ReadView const&, beast::Journal const&);
+};
+
+}  // namespace xrpl

include/xrpl/tx/invariants/LoanInvariant.h

@@ -1,57 +1,14 @@
 #pragma once
 
-#include <xrpl/basics/base_uint.h>
 #include <xrpl/beast/utility/Journal.h>
 #include <xrpl/ledger/ReadView.h>
 #include <xrpl/protocol/STTx.h>
 #include <xrpl/protocol/TER.h>
 
-#include <map>
 #include <vector>
 
 namespace xrpl {
 
-/**
- * @brief Invariants: Loan brokers are internally consistent
- *
- * 1. If `LoanBroker.OwnerCount = 0` the `DirectoryNode` will have at most one
- *    node (the root), which will only hold entries for `RippleState` or
- * `MPToken` objects.
- *
- */
-class ValidLoanBroker
-{
-    // Not all of these elements will necessarily be populated. Remaining items
-    // will be looked up as needed.
-    struct BrokerInfo
-    {
-        SLE::const_pointer brokerBefore = nullptr;
-        // After is used for most of the checks, except
-        // those that check changed values.
-        SLE::const_pointer brokerAfter = nullptr;
-    };
-    // Collect all the LoanBrokers found directly or indirectly through
-    // pseudo-accounts. Key is the brokerID / index. It will be used to find the
-    // LoanBroker object if brokerBefore and brokerAfter are nullptr
-    std::map<uint256, BrokerInfo> brokers_;
-    // Collect all the modified trust lines. Their high and low accounts will be
-    // loaded to look for LoanBroker pseudo-accounts.
-    std::vector<SLE::const_pointer> lines_;
-    // Collect all the modified MPTokens. Their accounts will be loaded to look
-    // for LoanBroker pseudo-accounts.
-    std::vector<SLE::const_pointer> mpts_;
-
-    static bool
-    goodZeroDirectory(ReadView const& view, SLE::const_ref dir, beast::Journal const& j);
-
-public:
-    void
-    visitEntry(bool, std::shared_ptr<SLE const> const&, std::shared_ptr<SLE const> const&);
-
-    bool
-    finalize(STTx const&, TER const, XRPAmount const, ReadView const&, beast::Journal const&);
-};
-
 /**
  * @brief Invariants: Loans are internally consistent
  *

src/libxrpl/tx/invariants/LoanBrokerInvariant.cpp

@@ -0,0 +1,194 @@
+#include <xrpl/tx/invariants/LoanBrokerInvariant.h>
+//
+#include <xrpl/basics/Log.h>
+#include <xrpl/beast/utility/instrumentation.h>
+#include <xrpl/ledger/View.h>
+#include <xrpl/ledger/helpers/RippleStateHelpers.h>
+#include <xrpl/protocol/Indexes.h>
+#include <xrpl/protocol/LedgerFormats.h>
+#include <xrpl/protocol/STNumber.h>
+#include <xrpl/protocol/TxFormats.h>
+
+namespace xrpl {
+
+void
+ValidLoanBroker::visitEntry(
+    bool isDelete,
+    std::shared_ptr<SLE const> const& before,
+    std::shared_ptr<SLE const> const& after)
+{
+    if (after)
+    {
+        if (after->getType() == ltLOAN_BROKER)
+        {
+            auto& broker = brokers_[after->key()];
+            broker.brokerBefore = before;
+            broker.brokerAfter = after;
+        }
+        else if (after->getType() == ltACCOUNT_ROOT && after->isFieldPresent(sfLoanBrokerID))
+        {
+            auto const& loanBrokerID = after->at(sfLoanBrokerID);
+            // create an entry if one doesn't already exist
+            brokers_.emplace(loanBrokerID, BrokerInfo{});
+        }
+        else if (after->getType() == ltRIPPLE_STATE)
+        {
+            lines_.emplace_back(after);
+        }
+        else if (after->getType() == ltMPTOKEN)
+        {
+            mpts_.emplace_back(after);
+        }
+    }
+}
+
+bool
+ValidLoanBroker::goodZeroDirectory(
+    ReadView const& view,
+    SLE::const_ref dir,
+    beast::Journal const& j)
+{
+    auto const next = dir->at(~sfIndexNext);
+    auto const prev = dir->at(~sfIndexPrevious);
+    if ((prev && (*prev != 0u)) || (next && (*next != 0u)))
+    {
+        JLOG(j.fatal()) << "Invariant failed: Loan Broker with zero "
+                           "OwnerCount has multiple directory pages";
+        return false;
+    }
+    auto indexes = dir->getFieldV256(sfIndexes);
+    if (indexes.size() > 1)
+    {
+        JLOG(j.fatal()) << "Invariant failed: Loan Broker with zero "
+                           "OwnerCount has multiple indexes in the Directory root";
+        return false;
+    }
+    if (indexes.size() == 1)
+    {
+        auto const index = indexes.value().front();
+        auto const sle = view.read(keylet::unchecked(index));
+        if (!sle)
+        {
+            JLOG(j.fatal()) << "Invariant failed: Loan Broker directory corrupt";
+            return false;
+        }
+        if (sle->getType() != ltRIPPLE_STATE && sle->getType() != ltMPTOKEN)
+        {
+            JLOG(j.fatal()) << "Invariant failed: Loan Broker with zero "
+                               "OwnerCount has an unexpected entry in the directory";
+            return false;
+        }
+    }
+
+    return true;
+}
+
+bool
+ValidLoanBroker::finalize(
+    STTx const& tx,
+    TER const,
+    XRPAmount const,
+    ReadView const& view,
+    beast::Journal const& j)
+{
+    // Loan Brokers will not exist on ledger if the Lending Protocol amendment
+    // is not enabled, so there's no need to check it.
+
+    for (auto const& line : lines_)
+    {
+        for (auto const& field : {&sfLowLimit, &sfHighLimit})
+        {
+            auto const account = view.read(keylet::account(line->at(*field).getIssuer()));
+            // This Invariant doesn't know about the rules for Trust Lines, so
+            // if the account is missing, don't treat it as an error. This
+            // loop is only concerned with finding Broker pseudo-accounts
+            if (account && account->isFieldPresent(sfLoanBrokerID))
+            {
+                auto const& loanBrokerID = account->at(sfLoanBrokerID);
+                // create an entry if one doesn't already exist
+                brokers_.emplace(loanBrokerID, BrokerInfo{});
+            }
+        }
+    }
+    for (auto const& mpt : mpts_)
+    {
+        auto const account = view.read(keylet::account(mpt->at(sfAccount)));
+        // This Invariant doesn't know about the rules for MPTokens, so
+        // if the account is missing, don't treat is as an error. This
+        // loop is only concerned with finding Broker pseudo-accounts
+        if (account && account->isFieldPresent(sfLoanBrokerID))
+        {
+            auto const& loanBrokerID = account->at(sfLoanBrokerID);
+            // create an entry if one doesn't already exist
+            brokers_.emplace(loanBrokerID, BrokerInfo{});
+        }
+    }
+
+    for (auto const& [brokerID, broker] : brokers_)
+    {
+        auto const& after =
+            broker.brokerAfter ? broker.brokerAfter : view.read(keylet::loanbroker(brokerID));
+
+        if (!after)
+        {
+            JLOG(j.fatal()) << "Invariant failed: Loan Broker missing";
+            return false;
+        }
+
+        auto const& before = broker.brokerBefore;
+
+        // https://github.com/Tapanito/XRPL-Standards/blob/xls-66-lending-protocol/XLS-0066d-lending-protocol/README.md#3123-invariants
+        // If `LoanBroker.OwnerCount = 0` the `DirectoryNode` will have at most
+        // one node (the root), which will only hold entries for `RippleState`
+        // or `MPToken` objects.
+        if (after->at(sfOwnerCount) == 0)
+        {
+            auto const dir = view.read(keylet::ownerDir(after->at(sfAccount)));
+            if (dir)
+            {
+                if (!goodZeroDirectory(view, dir, j))
+                {
+                    return false;
+                }
+            }
+        }
+        if (before && before->at(sfLoanSequence) > after->at(sfLoanSequence))
+        {
+            JLOG(j.fatal()) << "Invariant failed: Loan Broker sequence number "
+                               "decreased";
+            return false;
+        }
+        if (after->at(sfDebtTotal) < 0)
+        {
+            JLOG(j.fatal()) << "Invariant failed: Loan Broker debt total is negative";
+            return false;
+        }
+        if (after->at(sfCoverAvailable) < 0)
+        {
+            JLOG(j.fatal()) << "Invariant failed: Loan Broker cover available is negative";
+            return false;
+        }
+        auto const vault = view.read(keylet::vault(after->at(sfVaultID)));
+        if (!vault)
+        {
+            JLOG(j.fatal()) << "Invariant failed: Loan Broker vault ID is invalid";
+            return false;
+        }
+        auto const& vaultAsset = vault->at(sfAsset);
+        if (after->at(sfCoverAvailable) < accountHolds(
+                                              view,
+                                              after->at(sfAccount),
+                                              vaultAsset,
+                                              FreezeHandling::fhIGNORE_FREEZE,
+                                              AuthHandling::ahIGNORE_AUTH,
+                                              j))
+        {
+            JLOG(j.fatal()) << "Invariant failed: Loan Broker cover available "
+                               "is less than pseudo-account asset balance";
+            return false;
+        }
+    }
+    return true;
+}
+
+}  // namespace xrpl

src/libxrpl/tx/invariants/LoanInvariant.cpp

@@ -2,197 +2,11 @@
 //
 #include <xrpl/basics/Log.h>
 #include <xrpl/beast/utility/instrumentation.h>
-#include <xrpl/ledger/View.h>
-#include <xrpl/ledger/helpers/RippleStateHelpers.h>
-#include <xrpl/protocol/Indexes.h>
 #include <xrpl/protocol/LedgerFormats.h>
 #include <xrpl/protocol/STNumber.h>
-#include <xrpl/protocol/TxFormats.h>
 
 namespace xrpl {
 
-void
-ValidLoanBroker::visitEntry(
-    bool isDelete,
-    std::shared_ptr<SLE const> const& before,
-    std::shared_ptr<SLE const> const& after)
-{
-    if (after)
-    {
-        if (after->getType() == ltLOAN_BROKER)
-        {
-            auto& broker = brokers_[after->key()];
-            broker.brokerBefore = before;
-            broker.brokerAfter = after;
-        }
-        else if (after->getType() == ltACCOUNT_ROOT && after->isFieldPresent(sfLoanBrokerID))
-        {
-            auto const& loanBrokerID = after->at(sfLoanBrokerID);
-            // create an entry if one doesn't already exist
-            brokers_.emplace(loanBrokerID, BrokerInfo{});
-        }
-        else if (after->getType() == ltRIPPLE_STATE)
-        {
-            lines_.emplace_back(after);
-        }
-        else if (after->getType() == ltMPTOKEN)
-        {
-            mpts_.emplace_back(after);
-        }
-    }
-}
-
-bool
-ValidLoanBroker::goodZeroDirectory(
-    ReadView const& view,
-    SLE::const_ref dir,
-    beast::Journal const& j)
-{
-    auto const next = dir->at(~sfIndexNext);
-    auto const prev = dir->at(~sfIndexPrevious);
-    if ((prev && (*prev != 0u)) || (next && (*next != 0u)))
-    {
-        JLOG(j.fatal()) << "Invariant failed: Loan Broker with zero "
-                           "OwnerCount has multiple directory pages";
-        return false;
-    }
-    auto indexes = dir->getFieldV256(sfIndexes);
-    if (indexes.size() > 1)
-    {
-        JLOG(j.fatal()) << "Invariant failed: Loan Broker with zero "
-                           "OwnerCount has multiple indexes in the Directory root";
-        return false;
-    }
-    if (indexes.size() == 1)
-    {
-        auto const index = indexes.value().front();
-        auto const sle = view.read(keylet::unchecked(index));
-        if (!sle)
-        {
-            JLOG(j.fatal()) << "Invariant failed: Loan Broker directory corrupt";
-            return false;
-        }
-        if (sle->getType() != ltRIPPLE_STATE && sle->getType() != ltMPTOKEN)
-        {
-            JLOG(j.fatal()) << "Invariant failed: Loan Broker with zero "
-                               "OwnerCount has an unexpected entry in the directory";
-            return false;
-        }
-    }
-
-    return true;
-}
-
-bool
-ValidLoanBroker::finalize(
-    STTx const& tx,
-    TER const,
-    XRPAmount const,
-    ReadView const& view,
-    beast::Journal const& j)
-{
-    // Loan Brokers will not exist on ledger if the Lending Protocol amendment
-    // is not enabled, so there's no need to check it.
-
-    for (auto const& line : lines_)
-    {
-        for (auto const& field : {&sfLowLimit, &sfHighLimit})
-        {
-            auto const account = view.read(keylet::account(line->at(*field).getIssuer()));
-            // This Invariant doesn't know about the rules for Trust Lines, so
-            // if the account is missing, don't treat it as an error. This
-            // loop is only concerned with finding Broker pseudo-accounts
-            if (account && account->isFieldPresent(sfLoanBrokerID))
-            {
-                auto const& loanBrokerID = account->at(sfLoanBrokerID);
-                // create an entry if one doesn't already exist
-                brokers_.emplace(loanBrokerID, BrokerInfo{});
-            }
-        }
-    }
-    for (auto const& mpt : mpts_)
-    {
-        auto const account = view.read(keylet::account(mpt->at(sfAccount)));
-        // This Invariant doesn't know about the rules for MPTokens, so
-        // if the account is missing, don't treat is as an error. This
-        // loop is only concerned with finding Broker pseudo-accounts
-        if (account && account->isFieldPresent(sfLoanBrokerID))
-        {
-            auto const& loanBrokerID = account->at(sfLoanBrokerID);
-            // create an entry if one doesn't already exist
-            brokers_.emplace(loanBrokerID, BrokerInfo{});
-        }
-    }
-
-    for (auto const& [brokerID, broker] : brokers_)
-    {
-        auto const& after =
-            broker.brokerAfter ? broker.brokerAfter : view.read(keylet::loanbroker(brokerID));
-
-        if (!after)
-        {
-            JLOG(j.fatal()) << "Invariant failed: Loan Broker missing";
-            return false;
-        }
-
-        auto const& before = broker.brokerBefore;
-
-        // https://github.com/Tapanito/XRPL-Standards/blob/xls-66-lending-protocol/XLS-0066d-lending-protocol/README.md#3123-invariants
-        // If `LoanBroker.OwnerCount = 0` the `DirectoryNode` will have at most
-        // one node (the root), which will only hold entries for `RippleState`
-        // or `MPToken` objects.
-        if (after->at(sfOwnerCount) == 0)
-        {
-            auto const dir = view.read(keylet::ownerDir(after->at(sfAccount)));
-            if (dir)
-            {
-                if (!goodZeroDirectory(view, dir, j))
-                {
-                    return false;
-                }
-            }
-        }
-        if (before && before->at(sfLoanSequence) > after->at(sfLoanSequence))
-        {
-            JLOG(j.fatal()) << "Invariant failed: Loan Broker sequence number "
-                               "decreased";
-            return false;
-        }
-        if (after->at(sfDebtTotal) < 0)
-        {
-            JLOG(j.fatal()) << "Invariant failed: Loan Broker debt total is negative";
-            return false;
-        }
-        if (after->at(sfCoverAvailable) < 0)
-        {
-            JLOG(j.fatal()) << "Invariant failed: Loan Broker cover available is negative";
-            return false;
-        }
-        auto const vault = view.read(keylet::vault(after->at(sfVaultID)));
-        if (!vault)
-        {
-            JLOG(j.fatal()) << "Invariant failed: Loan Broker vault ID is invalid";
-            return false;
-        }
-        auto const& vaultAsset = vault->at(sfAsset);
-        if (after->at(sfCoverAvailable) < accountHolds(
-                                              view,
-                                              after->at(sfAccount),
-                                              vaultAsset,
-                                              FreezeHandling::fhIGNORE_FREEZE,
-                                              AuthHandling::ahIGNORE_AUTH,
-                                              j))
-        {
-            JLOG(j.fatal()) << "Invariant failed: Loan Broker cover available "
-                               "is less than pseudo-account asset balance";
-            return false;
-        }
-    }
-    return true;
-}
-
-//------------------------------------------------------------------------------
-
 void
 ValidLoan::visitEntry(
     bool isDelete,