Kernel: Verify interrupts are disabled when interacting with Mutexes

This should help prevent deadlocks where a thread blocks on a Mutex
while interrupts are disabled, and makes it impossible for the holder of
the Mutex to make forward progress because it cannot be scheduled in.

Hide it behind a new debug macro LOCK_IN_CRITICAL_DEBUG for now, because
Ext2FS takes a series of Mutexes from the page fault handler, which
executes with interrupts disabled.

Kernel/Debug.h.in

@@ -166,6 +166,10 @@
 #cmakedefine01 LOCK_DEBUG
 #endif
 
+#ifndef LOCK_IN_CRITICAL_DEBUG
+#cmakedefine01 LOCK_IN_CRITICAL_DEBUG
+#endif
+
 #ifndef LOCK_RESTORE_DEBUG
 #cmakedefine01 LOCK_RESTORE_DEBUG
 #endif

Kernel/Locking/Mutex.cpp

@@ -18,6 +18,8 @@ void Mutex::lock(Mode mode, [[maybe_unused]] LockLocation const& location)
  // NOTE: This may be called from an interrupt handler (not an IRQ handler)
  // and also from within critical sections!
  VERIFY(!Processor::current_in_irq());
+ if constexpr (LOCK_IN_CRITICAL_DEBUG)
+ VERIFY_INTERRUPTS_ENABLED();
  VERIFY(mode != Mode::Unlocked);
  auto current_thread = Thread::current();
 
@@ -143,6 +145,8 @@ void Mutex::unlock()
 {
  // NOTE: This may be called from an interrupt handler (not an IRQ handler)
  // and also from within critical sections!
+ if constexpr (LOCK_IN_CRITICAL_DEBUG)
+ VERIFY_INTERRUPTS_ENABLED();
  VERIFY(!Processor::current_in_irq());
  auto current_thread = Thread::current();
  SpinlockLocker lock(m_lock);
@@ -198,6 +202,8 @@ void Mutex::unlock()
 
 void Mutex::block(Thread& current_thread, Mode mode, SpinlockLocker<Spinlock<u8>>& lock, u32 requested_locks)
 {
+ if constexpr (LOCK_IN_CRITICAL_DEBUG)
+ VERIFY_INTERRUPTS_ENABLED();
  auto& blocked_thread_list = thread_list_for_mode(mode);
  VERIFY(!blocked_thread_list.contains(current_thread));
  blocked_thread_list.append(current_thread);

Meta/CMake/all_the_debug_macros.cmake

@@ -101,6 +101,7 @@ set(LEXER_DEBUG ON)
 set(LINE_EDITOR_DEBUG ON)
 set(LOCAL_SOCKET_DEBUG ON)
 set(LOCK_DEBUG ON)
+set(LOCK_IN_CRITICAL_DEBUG ON)
 set(LOCK_RESTORE_DEBUG ON)
 set(LOCK_TRACE_DEBUG ON)
 set(LOOKUPSERVER_DEBUG ON)