From 41ead20bfb32f03c1b36bd4e98bdcb569345dba1 Mon Sep 17 00:00:00 2001
From: Nikolay Nikolov <nickysn@gmail.com>
Date: Sat, 3 Aug 2024 02:34:00 +0300
Subject: [PATCH] * WebAssembly threads: fixed race condition LockMutex in the
 check where Locked   is 1, but Owner still holds the current thread id, even
 though another thread   has just acquired a lock, but still haven't updated
 the owner thread ID. We   avoid this problem by setting Owner to nil before
 unlocking the mutex. And in   InitMutex/DoneMutex, we store the creator
 thread ID in a different field -   Creator, instead of Owner.

---
 rtl/wasi/sysosh.inc    | 3 ++-
 rtl/wasi/wasmmutex.inc | 5 +++--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/rtl/wasi/sysosh.inc b/rtl/wasi/sysosh.inc
index 1b7395daec..23af0955fc 100644
--- a/rtl/wasi/sysosh.inc
+++ b/rtl/wasi/sysosh.inc
@@ -27,6 +27,7 @@ type
     Count: LongInt; // Number of times locked.
     Waiters : LongInt; // Number of waiters
     Kind : LongInt; // Kind of mutex, Equals Ord(TMutexKind)
-    Owner : TThreadID;  // Owner thread
+    Owner : TThreadID;  // Owner thread (who holds the lock)
+    Creator : TThreadID;  // Creator thread
     Destroying : Boolean; // Set when notifying that we're destroying the mutex.
   end;
diff --git a/rtl/wasi/wasmmutex.inc b/rtl/wasi/wasmmutex.inc
index fab110b9d0..97f62d0e77 100644
--- a/rtl/wasi/wasmmutex.inc
+++ b/rtl/wasi/wasmmutex.inc
@@ -20,7 +20,7 @@ begin
   FillChar(M,SizeOf(TWasmMutex),0);
   if aOwner=Nil then
     aOwner:=GetSelfThread;
-  M.Owner:=aOwner;
+  M.Creator:=aOwner;
   M.Kind:=Ord(aKind);
 end;
 
@@ -30,7 +30,7 @@ Var
   a : LongInt;
 
 begin
-  if (M.Locked>0) and (M.Owner=GetSelfThread) then
+  if (M.Locked>0) and (M.Creator=GetSelfThread) then
     begin
     M.Destroying:=True;
     a:=fpc_wasm32_memory_atomic_notify(@M.Locked,MaxThreadSignal);
@@ -190,6 +190,7 @@ begin
       InterLockedDecrement(M.Count);
     if (M.Count=0) then
       begin
+        M.Owner:=nil;
         M.Locked:=0;
         a:=fpc_wasm32_memory_atomic_notify(@M.Locked,1);
       end;