From 239bb9cf654ecf9c8c3ccdb7fd4d00eb146595f2 Mon Sep 17 00:00:00 2001
From: VivekSainiEQ <vivek@eqalpha.com>
Date: Mon, 29 Mar 2021 18:46:06 +0000
Subject: [PATCH] Added logic back to only acquire/release GIL if modules are
 enabled, without causing deadlocks

Former-commit-id: 9ab36ddc36e1d12e41d2eca917ee24a44a82df52
---
 src/server.cpp | 12 ++++++++----
 src/server.h   |  2 ++
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/server.cpp b/src/server.cpp
index 48b0cf89d..2f7fdb704 100644
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -2401,8 +2401,10 @@ void beforeSleep(struct aeEventLoop *eventLoop) {
     locker.disarm();
     if (!fSentReplies)
         handleClientsWithPendingWrites(iel, aof_state);
-    moduleReleaseGIL(TRUE /*fServerThread*/);
-
+    /* Determine whether the modules are enabled before sleeping, and use that result
+       both here, and after wakeup to avoid double acquire or release of the GIL */
+    serverTL->modulesEnabledThisAeLoop = !!moduleCount();
+    if (serverTL->modulesEnabledThisAeLoop) moduleReleaseGIL(TRUE /*fServerThread*/);
     /* Do NOT add anything below moduleReleaseGIL !!! */
 }
 
@@ -2413,8 +2415,10 @@ void afterSleep(struct aeEventLoop *eventLoop) {
     UNUSED(eventLoop);
     /* Do NOT add anything above moduleAcquireGIL !!! */
 
-    /* Aquire the modules GIL so that their threads won't touch anything. */
-    moduleAcquireGIL(TRUE /*fServerThread*/);
+    /* Aquire the modules GIL so that their threads won't touch anything. 
+       Don't check here that modules are enabled, rather use the result from beforeSleep
+       Otherwise you may double acquire the GIL and cause deadlocks in the module */
+    if (serverTL->modulesEnabledThisAeLoop) moduleAcquireGIL(TRUE /*fServerThread*/);
 }
 
 /* =========================== Server initialization ======================== */
diff --git a/src/server.h b/src/server.h
index bc3b62fb4..a0ee1bfc0 100644
--- a/src/server.h
+++ b/src/server.h
@@ -1389,6 +1389,8 @@ struct redisServerThreadVars {
     char neterr[ANET_ERR_LEN];   /* Error buffer for anet.c */
     long unsigned commandsExecuted = 0;
     bool fRetrySetAofEvent = false;
+    bool modulesEnabledThisAeLoop = false; /* In this loop of aeMain, were modules enabled before 
+                                              the thread went to sleep? */
     std::vector<client*> vecclientsProcess;
     dictAsyncRehashCtl *rehashCtl = nullptr;
 };