From d4ba15571105723e2bf8120e5cf8ca440261029c Mon Sep 17 00:00:00 2001
From: Andreas Kling <awesomekling@gmail.com>
Date: Fri, 8 Feb 2019 16:40:48 +0100
Subject: Kernel: Break retain cycle between Inode and VMObject.

There's no need for an Inode to keep its corresponding VMObject alive.
Obviously there are huge benefits to keeping a filesystem cache,
but leaking everything is hardly the right strategy. :^)
---
 Kernel/FileSystem.cpp    | 4 ++--
 Kernel/FileSystem.h      | 5 +++--
 Kernel/MemoryManager.cpp | 6 ++----
 Kernel/MemoryManager.h   | 3 ++-
 4 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/Kernel/FileSystem.cpp b/Kernel/FileSystem.cpp
index 953ef55abe..75e6a83e04 100644
--- a/Kernel/FileSystem.cpp
+++ b/Kernel/FileSystem.cpp
@@ -148,7 +148,7 @@ void FS::sync()
     }
 }
 
-void Inode::set_vmo(RetainPtr<VMObject>&& vmo)
+void Inode::set_vmo(VMObject& vmo)
 {
-    m_vmo = move(vmo);
+    m_vmo = vmo.make_weak_ptr();
 }
diff --git a/Kernel/FileSystem.h b/Kernel/FileSystem.h
index 58a24d25cb..eab654ac51 100644
--- a/Kernel/FileSystem.h
+++ b/Kernel/FileSystem.h
@@ -14,6 +14,7 @@
 #include <AK/Function.h>
 #include <AK/kstdio.h>
 #include <AK/Lock.h>
+#include <AK/WeakPtr.h>
 
 static const dword mepoch = 476763780;
 
@@ -103,7 +104,7 @@ public:
 
     void will_be_destroyed();
 
-    void set_vmo(RetainPtr<VMObject>&&);
+    void set_vmo(VMObject&);
     VMObject* vmo() { return m_vmo.ptr(); }
     const VMObject* vmo() const { return m_vmo.ptr(); }
 
@@ -118,7 +119,7 @@ protected:
 private:
     FS& m_fs;
     unsigned m_index { 0 };
-    RetainPtr<VMObject> m_vmo;
+    WeakPtr<VMObject> m_vmo;
     bool m_metadata_dirty { false };
 };
 
diff --git a/Kernel/MemoryManager.cpp b/Kernel/MemoryManager.cpp
index 7f70203959..76dacee97c 100644
--- a/Kernel/MemoryManager.cpp
+++ b/Kernel/MemoryManager.cpp
@@ -667,7 +667,7 @@ RetainPtr<VMObject> VMObject::create_file_backed(RetainPtr<Inode>&& inode)
     if (inode->vmo())
         return static_cast<VMObject*>(inode->vmo());
     auto vmo = adopt(*new VMObject(move(inode)));
-    vmo->inode()->set_vmo(vmo.ptr());
+    vmo->inode()->set_vmo(*vmo);
     return vmo;
 }
 
@@ -732,10 +732,8 @@ VMObject::VMObject(RetainPtr<Inode>&& inode)
 
 VMObject::~VMObject()
 {
-    if (m_inode) {
+    if (m_inode)
         ASSERT(m_inode->vmo() == this);
-        m_inode->set_vmo(nullptr);
-    }
     MM.unregister_vmo(*this);
 }
 
diff --git a/Kernel/MemoryManager.h b/Kernel/MemoryManager.h
index b5974c3d67..a7243d5b97 100644
--- a/Kernel/MemoryManager.h
+++ b/Kernel/MemoryManager.h
@@ -10,6 +10,7 @@
 #include <AK/HashTable.h>
 #include <AK/AKString.h>
 #include <AK/Badge.h>
+#include <AK/Weakable.h>
 #include <Kernel/VirtualFileSystem.h>
 
 #define PAGE_ROUND_UP(x) ((((dword)(x)) + PAGE_SIZE-1) & (~(PAGE_SIZE-1)))
@@ -77,7 +78,7 @@ private:
     HashMap<unsigned, RetainPtr<PhysicalPage>> m_physical_pages;
 };
 
-class VMObject : public Retainable<VMObject> {
+class VMObject : public Retainable<VMObject>, public Weakable<VMObject> {
     friend class MemoryManager;
 public:
     static RetainPtr<VMObject> create_file_backed(RetainPtr<Inode>&&);
-- 
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