From a6e4c504e2a06bf25ca14e239ff942ae89935a05 Mon Sep 17 00:00:00 2001
From: Andreas Kling <awesomekling@gmail.com>
Date: Thu, 10 Oct 2019 11:56:57 +0200
Subject: [PATCH] Kernel: Make SlabAllocator fall back to kmalloc() when slabs
 run out

This is obviously not ideal, and it would be better to teach it how to
allocate more pages, etc. But since the physical page allocator itself
currently uses SlabAllocator, it's a little bit tricky :^)
---
 Kernel/Heap/SlabAllocator.cpp | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/Kernel/Heap/SlabAllocator.cpp b/Kernel/Heap/SlabAllocator.cpp
index 6b886db4fc..39b346b376 100644
--- a/Kernel/Heap/SlabAllocator.cpp
+++ b/Kernel/Heap/SlabAllocator.cpp
@@ -10,8 +10,9 @@ public:
 
     void init(size_t size)
     {
-        void* base = kmalloc_eternal(size);
-        FreeSlab* slabs = (FreeSlab*)base;
+        m_base = kmalloc_eternal(size);
+        m_end = (u8*)m_base + size;
+        FreeSlab* slabs = (FreeSlab*)m_base;
         size_t slab_count = size / templated_slab_size;
         for (size_t i = 1; i < slab_count; ++i) {
             slabs[i].next = &slabs[i - 1];
@@ -27,6 +28,8 @@ public:
     void* alloc()
     {
         InterruptDisabler disabler;
+        if (!m_freelist)
+            return kmalloc(slab_size());
         ASSERT(m_freelist);
         void* ptr = m_freelist;
         m_freelist = m_freelist->next;
@@ -39,6 +42,10 @@ public:
     {
         InterruptDisabler disabler;
         ASSERT(ptr);
+        if (ptr < m_base || ptr >= m_end) {
+            kfree(ptr);
+            return;
+        }
         ((FreeSlab*)ptr)->next = m_freelist;
         m_freelist = (FreeSlab*)ptr;
         ++m_num_allocated;
@@ -57,6 +64,8 @@ private:
     FreeSlab* m_freelist { nullptr };
     size_t m_num_allocated { 0 };
     size_t m_num_free { 0 };
+    void* m_base { nullptr };
+    void* m_end { nullptr };
 
     static_assert(sizeof(FreeSlab) == templated_slab_size);
 };