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Kernel: Simplify VMObject locking & page fault handlers

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This patch greatly simplifies VMObject locking by doing two things:

1. Giving VMObject an IntrusiveList of all its mapping Region objects.
2. Removing VMObject::m_paging_lock in favor of VMObject::m_lock

Before (1), VMObject::for_each_region() was forced to acquire the
global MM lock (since it worked by walking MemoryManager's list of
all regions and checking for regions that pointed to itself.)

With each VMObject having its own list of Regions, VMObject's own
m_lock is all we need.

Before (2), page fault handlers used a separate mutex for preventing
overlapping work. This design required multiple temporary unlocks
and was generally extremely hard to reason about.

Instead, page fault handlers now use VMObject's own m_lock as well.
This commit is contained in:
Andreas Kling 2021-07-23 02:40:16 +02:00
parent 64babcaa83
commit 082ed6f417
10 changed files with 116 additions and 155 deletions
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43
Kernel/VM/VMObject.h
View file

@ -15,6 +15,7 @@
#include <AK/Weakable.h>
#include <Kernel/Forward.h>
#include <Kernel/Mutex.h>
#include <Kernel/VM/Region.h>
namespace Kernel {
@ -48,8 +49,20 @@ public:
virtual StringView class_name() const = 0;
ALWAYS_INLINE void ref_region() { m_regions_count++; }
ALWAYS_INLINE void unref_region() { m_regions_count--; }
ALWAYS_INLINE void add_region(Region& region)
{
ScopedSpinLock locker(m_lock);
m_regions_count++;
m_regions.append(region);
}
ALWAYS_INLINE void remove_region(Region& region)
{
ScopedSpinLock locker(m_lock);
m_regions_count--;
m_regions.remove(region);
}
ALWAYS_INLINE bool is_shared_by_multiple_regions() const { return m_regions_count > 1; }
void register_on_deleted_handler(VMObjectDeletedHandler& handler)
@ -70,9 +83,8 @@ protected:
IntrusiveListNode<VMObject> m_list_node;
FixedArray<RefPtr<PhysicalPage>> m_physical_pages;
Mutex m_paging_lock { "VMObject" };
mutable SpinLock<u8> m_lock;
mutable RecursiveSpinLock m_lock;
private:
VMObject& operator=(VMObject const&) = delete;
@ -83,8 +95,31 @@ private:
HashTable<VMObjectDeletedHandler*> m_on_deleted;
SpinLock<u8> m_on_deleted_lock;
Region::ListInVMObject m_regions;
public:
using List = IntrusiveList<VMObject, RawPtr<VMObject>, &VMObject::m_list_node>;
};
template<typename Callback>
inline void VMObject::for_each_region(Callback callback)
{
ScopedSpinLock lock(m_lock);
for (auto& region : m_regions) {
callback(region);
}
}
inline PhysicalPage const* Region::physical_page(size_t index) const
{
VERIFY(index < page_count());
return vmobject().physical_pages()[first_page_index() + index];
}
inline RefPtr<PhysicalPage>& Region::physical_page_slot(size_t index)
{
VERIFY(index < page_count());
return vmobject().physical_pages()[first_page_index() + index];
}
}