From fad8e7fba7bf2c523a191309d392cab79668264b Mon Sep 17 00:00:00 2001
From: MarcoFalke <*~=`'#}+{/-|&$^_@721217.xyz>
Date: Mon, 30 Sep 2024 11:53:05 +0200
Subject: [PATCH] bugfix: Mark m_tip_block_cv as guarded by m_tip_block_mutex

This is not strictly required, but all places using m_tip_block_cv
(except shutdown) already take the lock. The annotation makes it easier
to catch potential deadlocks before review.

Adding the missing lock to the shutdown sequence is a bugfix.

An alternative would be to take the lock and release it before
notifying, see
https://github.com/bitcoin/bitcoin/pull/30967#discussion_r1778899716
---
 src/node/kernel_notifications.h | 2 +-
 src/rpc/server.cpp              | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/node/kernel_notifications.h b/src/node/kernel_notifications.h
index 71947e5f98c..12017f2b2c2 100644
--- a/src/node/kernel_notifications.h
+++ b/src/node/kernel_notifications.h
@@ -58,7 +58,7 @@ public:
     bool m_shutdown_on_fatal_error{true};
 
     Mutex m_tip_block_mutex;
-    std::condition_variable m_tip_block_cv;
+    std::condition_variable m_tip_block_cv GUARDED_BY(m_tip_block_mutex);
     //! The block for which the last blockTip notification was received for.
     uint256 m_tip_block GUARDED_BY(m_tip_block_mutex);
 
diff --git a/src/rpc/server.cpp b/src/rpc/server.cpp
index 086f609ac3e..ab2135a9193 100644
--- a/src/rpc/server.cpp
+++ b/src/rpc/server.cpp
@@ -305,7 +305,7 @@ void StopRPC(const std::any& context)
         DeleteAuthCookie();
         node::NodeContext& node = EnsureAnyNodeContext(context);
         // The notifications interface doesn't exist between initialization step 4a and 7.
-        if (node.notifications) node.notifications->m_tip_block_cv.notify_all();
+        if (node.notifications) WITH_LOCK(node.notifications->m_tip_block_mutex, node.notifications->m_tip_block_cv.notify_all());
         LogDebug(BCLog::RPC, "RPC stopped.\n");
     });
 }