From 2a35741064339fa7e3f7f54373e583211a24d068 Mon Sep 17 00:00:00 2001
From: Harris Brakmic <brakmic@gmail.com>
Date: Sat, 22 Jul 2017 15:23:03 +0200
Subject: [PATCH] Changes in potential_deadlock_detected behavior

---
 src/sync.cpp | 62 +++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 49 insertions(+), 13 deletions(-)

diff --git a/src/sync.cpp b/src/sync.cpp
index e624a9ee8499b..d3c74ba67ca57 100644
--- a/src/sync.cpp
+++ b/src/sync.cpp
@@ -59,21 +59,57 @@ static boost::thread_specific_ptr<LockStack> lockstack;
 
 static void potential_deadlock_detected(const std::pair<void*, void*>& mismatch, const LockStack& s1, const LockStack& s2)
 {
-    LogPrintf("POTENTIAL DEADLOCK DETECTED\n");
-    LogPrintf("Previous lock order was:\n");
-    BOOST_FOREACH(const PAIRTYPE(void*, CLockLocation)& i, s2)
-    {
-        if (i.first == mismatch.first) LogPrintf(" (1)");
-        if (i.first == mismatch.second) LogPrintf(" (2)");
-        LogPrintf(" %s\n", i.second.ToString());
+    // We attempt to not assert on probably-not deadlocks by assuming that
+    // a try lock will immediately have otherwise bailed if it had
+    // failed to get the lock
+    // We do this by, for the locks which triggered the potential deadlock,
+    // in either lockorder, checking that the second of the two which is locked
+    // is only a TRY_LOCK, ignoring locks if they are reentrant.
+    bool firstLocked = false;
+    bool secondLocked = false;
+    bool onlyMaybeDeadlock = false;
+    std::string strOutput = "";
+
+    strOutput += "POTENTIAL DEADLOCK DETECTED\n";
+    strOutput += "Previous lock order was:\n";
+    BOOST_FOREACH (const PAIRTYPE(void*, CLockLocation) & i, s2) {
+        if (i.first == mismatch.first) {
+            strOutput += " (1)";
+            if (!firstLocked && secondLocked && i.second.fTry)
+                onlyMaybeDeadlock = true;
+            firstLocked = true;
+        }
+        if (i.first == mismatch.second) {
+            strOutput += " (2)";
+            if (!secondLocked && firstLocked && i.second.fTry)
+                onlyMaybeDeadlock = true;
+            secondLocked = true;
+        }
+        strOutput += strprintf(" %s\n", i.second.ToString().c_str());
     }
-    LogPrintf("Current lock order is:\n");
-    BOOST_FOREACH(const PAIRTYPE(void*, CLockLocation)& i, s1)
-    {
-        if (i.first == mismatch.first) LogPrintf(" (1)");
-        if (i.first == mismatch.second) LogPrintf(" (2)");
-        LogPrintf(" %s\n", i.second.ToString());
+    firstLocked = false;
+    secondLocked = false;
+    strOutput += "Current lock order is:\n";
+    BOOST_FOREACH (const PAIRTYPE(void*, CLockLocation) & i, s1) {
+        if (i.first == mismatch.first) {
+            strOutput += " (1)";
+            if (!firstLocked && secondLocked && i.second.fTry)
+                onlyMaybeDeadlock = true;
+            firstLocked = true;
+        }
+        if (i.first == mismatch.second) {
+            strOutput += " (2)";
+            if (!secondLocked && firstLocked && i.second.fTry)
+                onlyMaybeDeadlock = true;
+            secondLocked = true;
+        }
+        strOutput += strprintf(" %s\n", i.second.ToString().c_str());
+    }
+    if(!onlyMaybeDeadlock) {
+        printf("%s\n", strOutput.c_str());
+        LogPrintf("%s\n", strOutput.c_str());
     }
+    assert(onlyMaybeDeadlock);
 }
 
 static void push_lock(void* c, const CLockLocation& locklocation, bool fTry)