Kernel: Add an InterruptFlagSaver helper class.

This is useful instead of InterruptDisabler in some cases.

Kernel/MemoryManager.cpp

@@ -304,12 +304,11 @@ bool MemoryManager::page_in_from_inode(Region& region, unsigned page_index_in_re
 
     auto& vmo_page = vmo.physical_pages()[region.first_page_index() + page_index_in_region];
 
-    // FIXME: Maybe this should have a separate class like InterruptFlagSaver?
+    InterruptFlagSaver saver;
-    InterruptDisabler disabler;
 
-    disabler.temporarily_sti();
+    sti();
     LOCKER(vmo.m_paging_lock);
-    disabler.temporarily_cli();
+    cli();
 
     if (!vmo_page.is_null()) {
         kprintf("MM: page_in_from_inode() but page already present. Fine with me!\n");
@@ -320,7 +319,7 @@ bool MemoryManager::page_in_from_inode(Region& region, unsigned page_index_in_re
 #ifdef MM_DEBUG
     dbgprintf("MM: page_in_from_inode ready to read from inode\n");
 #endif
-    disabler.temporarily_sti();
+    sti();
     byte page_buffer[PAGE_SIZE];
     auto& inode = *vmo.inode();
     auto nread = inode.read_bytes(vmo.inode_offset() + ((region.first_page_index() + page_index_in_region) * PAGE_SIZE), PAGE_SIZE, page_buffer, nullptr);
@@ -332,7 +331,7 @@ bool MemoryManager::page_in_from_inode(Region& region, unsigned page_index_in_re
         // If we read less than a page, zero out the rest to avoid leaking uninitialized data.
         memset(page_buffer + nread, 0, PAGE_SIZE - nread);
     }
-    disabler.temporarily_cli();
+    cli();
     vmo_page = allocate_physical_page(ShouldZeroFill::No);
     if (vmo_page.is_null()) {
         kprintf("MM: page_in_from_inode was unable to allocate a physical page\n");

Kernel/Process.cpp

@@ -2181,10 +2181,10 @@ int Process::sys$chmod(const char* pathname, mode_t mode)
 
 void Process::die()
 {
+    destroy_all_windows();
     set_state(Dead);
     m_fds.clear();
     m_tty = nullptr;
-    destroy_all_windows();
 
     InterruptDisabler disabler;
     if (auto* parent_process = Process::from_pid(m_ppid)) {

Kernel/ProcessGUI.cpp

@@ -262,6 +262,8 @@ int Process::gui$set_global_cursor_tracking_enabled(int window_id, bool enabled)
 
 void Process::destroy_all_windows()
 {
+    InterruptFlagSaver saver;
+    sti();
     for (auto& it : m_windows) {
         auto message = make<WSMessage>(WSMessage::WM_DestroyWindow);
         it.value->notify_process_died(Badge<Process>());

Kernel/Scheduler.cpp

@@ -12,7 +12,7 @@ static const dword time_slice = 5; // *10 = 50ms
 Process* current;
 Process* g_last_fpu_process;
 static Process* s_colonel_process;
-static bool s_in_yield;
+static volatile bool s_in_yield;
 
 struct TaskRedirectionData {
     word selector;

Kernel/i386.h

@@ -106,6 +106,25 @@ inline bool are_interrupts_enabled()
     return cpu_flags() & 0x200;
 }
 
+class InterruptFlagSaver {
+public:
+    InterruptFlagSaver()
+    {
+        m_flags = cpu_flags();
+    }
+
+    ~InterruptFlagSaver()
+    {
+        if (m_flags & 0x200)
+            sti();
+        else
+            cli();
+    }
+
+private:
+    dword m_flags;
+};
+
 class InterruptDisabler {
 public:
     InterruptDisabler()
@@ -120,16 +139,6 @@ public:
             sti();
     }
 
-    void temporarily_cli()
-    {
-        cli();
-    }
-
-    void temporarily_sti()
-    {
-        sti();
-    }
-
 private:
     dword m_flags;
 };