Kernel: Fix inconsistent lock acquisition order in kmalloc

We always want to grab the page directory lock before the MM lock.
This fixes a deadlock I encountered when building DOOM with make -j4.

Kernel/Heap/kmalloc.cpp

@@ -332,8 +332,8 @@ struct KmallocGlobalData {
 
         auto cpu_supports_nx = Processor::current().has_nx();
 
-        SpinlockLocker mm_locker(Memory::s_mm_lock);
         SpinlockLocker pd_locker(MM.kernel_page_directory().get_lock());
+        SpinlockLocker mm_locker(Memory::s_mm_lock);
 
         for (auto vaddr = new_subheap_base; !physical_pages.is_empty(); vaddr = vaddr.offset(PAGE_SIZE)) {
             // FIXME: We currently leak physical memory when mapping it into the kmalloc heap.
@@ -365,8 +365,8 @@ struct KmallocGlobalData {
 
         // Make sure the entire kmalloc VM range is backed by page tables.
         // This avoids having to deal with lazy page table allocation during heap expansion.
-        SpinlockLocker mm_locker(Memory::s_mm_lock);
         SpinlockLocker pd_locker(MM.kernel_page_directory().get_lock());
+        SpinlockLocker mm_locker(Memory::s_mm_lock);
         for (auto vaddr = reserved_region->range().base(); vaddr < reserved_region->range().end(); vaddr = vaddr.offset(PAGE_SIZE)) {
             MM.ensure_pte(MM.kernel_page_directory(), vaddr);
         }