Make font loading use mmap().

This exposed a serious race condition in page_in_from_inode().
Reordered the logic and added a paging lock to VMObject.
Now, only one process can page in from a VMObject at a time.
There are definitely ways to optimize this, for instance by making
the locking be per-page instead. It's not something that I'm going
to worry about right now though.

1 files changed, 2 insertions, 0 deletions

diff --git a/Kernel/MemoryManager.h b/Kernel/MemoryManager.h
index 215ffc1a2e..de189e9f8d 100644
--- a/Kernel/MemoryManager.h
+++ b/Kernel/MemoryManager.h
@@ -77,6 +77,7 @@ private:
 };
 
 class VMObject : public Retainable<VMObject> {
+    friend class MemoryManager;
 public:
     static RetainPtr<VMObject> create_file_backed(RetainPtr<Inode>&&, size_t);
     static RetainPtr<VMObject> create_anonymous(size_t);
@@ -108,6 +109,7 @@ private:
     size_t m_size { 0 };
     RetainPtr<Inode> m_inode;
     Vector<RetainPtr<PhysicalPage>> m_physical_pages;
+    Lock m_paging_lock;
 };
 
 class Region : public Retainable<Region> {