Index: include/lldb/Utility/Log.h
===================================================================
--- include/lldb/Utility/Log.h
+++ include/lldb/Utility/Log.h
@@ -116,6 +116,11 @@
 
   static void DisableAllLogChannels();
 
+  // Only use if no other threads are executing and calling the locking version
+  // is known to be unsafe (for example, this happens right after forking, if we
+  // have forked while another thread was holding the log mutex)).
+  static void DisableAllLogChannelsUnlocked();
+
   static void ListAllLogChannels(llvm::raw_ostream &stream);
 
   //------------------------------------------------------------------
@@ -184,6 +189,7 @@
               uint32_t options, uint32_t flags);
 
   void Disable(uint32_t flags);
+  void DisableUnlocked(uint32_t flags);
 
   typedef llvm::StringMap<Log> ChannelMap;
   static llvm::ManagedStatic<ChannelMap> g_channel_map;
Index: source/Host/posix/ProcessLauncherPosixFork.cpp
===================================================================
--- source/Host/posix/ProcessLauncherPosixFork.cpp
+++ source/Host/posix/ProcessLauncherPosixFork.cpp
@@ -97,7 +97,7 @@
                                               const ProcessLaunchInfo &info) {
   // First, make sure we disable all logging. If we are logging to stdout, our
   // logs can be mistaken for inferior output.
-  Log::DisableAllLogChannels();
+  Log::DisableAllLogChannelsUnlocked();
 
   // Do not inherit setgid powers.
   if (setgid(getgid()) != 0)
Index: source/Utility/Log.cpp
===================================================================
--- source/Utility/Log.cpp
+++ source/Utility/Log.cpp
@@ -90,7 +90,10 @@
 
 void Log::Disable(uint32_t flags) {
   llvm::sys::ScopedWriter lock(m_mutex);
+  DisableUnlocked(flags);
+}
 
+void Log::DisableUnlocked(uint32_t flags) {
   uint32_t mask = m_mask.fetch_and(~flags, std::memory_order_relaxed);
   if (!(mask & ~flags)) {
     m_stream_sp.reset();
@@ -241,6 +244,11 @@
     entry.second.Disable(UINT32_MAX);
 }
 
+void Log::DisableAllLogChannelsUnlocked() {
+  for (auto &entry : *g_channel_map)
+    entry.second.DisableUnlocked(UINT32_MAX);
+}
+
 void Log::ListAllLogChannels(llvm::raw_ostream &stream) {
   if (g_channel_map->empty()) {
     stream << "No logging channels are currently registered.\n";