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.

1 files changed, 6 insertions, 0 deletions

diff --git a/Kernel/Locking/Mutex.cpp b/Kernel/Locking/Mutex.cpp
index 829001958b..14ad0f70ed 100644
--- a/Kernel/Locking/Mutex.cpp
+++ b/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);