Kernel: Remove old region from process' regions vector before splitting

This does not affect functionality right now, but it means that the
regions vector will now never have any overlapping regions, which will
allow the use of balance binary search trees instead of a vector in the
future. (since they require keys to be exclusive)

3 files changed, 36 insertions, 20 deletions

diff --git a/Kernel/Syscalls/mmap.cpp b/Kernel/Syscalls/mmap.cpp
index d818701629..db401a59c5 100644
--- a/Kernel/Syscalls/mmap.cpp
+++ b/Kernel/Syscalls/mmap.cpp
@@ -341,20 +341,24 @@ KResultOr<int> Process::sys$mprotect(Userspace<void*> addr, size_t size, int pro
             return EACCES;
         }
 
+        // Remove the old region from our regions tree, since were going to add another region
+        // with the exact same start address, but dont deallocate it yet
+        auto region = space().take_region(*old_region);
+        VERIFY(region);
+
+        // Unmap the old region here, specifying that we *don't* want the VM deallocated.
+        region->unmap(Region::ShouldDeallocateVirtualMemoryRange::No);
+
         // This vector is the region(s) adjacent to our range.
         // We need to allocate a new region for the range we wanted to change permission bits on.
-        auto adjacent_regions = space().split_region_around_range(*old_region, range_to_mprotect);
+        auto adjacent_regions = space().split_region_around_range(*region, range_to_mprotect);
 
-        size_t new_range_offset_in_vmobject = old_region->offset_in_vmobject() + (range_to_mprotect.base().get() - old_region->range().base().get());
-        auto& new_region = space().allocate_split_region(*old_region, range_to_mprotect, new_range_offset_in_vmobject);
+        size_t new_range_offset_in_vmobject = region->offset_in_vmobject() + (range_to_mprotect.base().get() - region->range().base().get());
+        auto& new_region = space().allocate_split_region(*region, range_to_mprotect, new_range_offset_in_vmobject);
         new_region.set_readable(prot & PROT_READ);
         new_region.set_writable(prot & PROT_WRITE);
         new_region.set_executable(prot & PROT_EXEC);
 
-        // Unmap the old region here, specifying that we *don't* want the VM deallocated.
-        old_region->unmap(Region::ShouldDeallocateVirtualMemoryRange::No);
-        space().deallocate_region(*old_region);
-
         // Map the new regions using our page directory (they were just allocated and don't have one).
         for (auto* adjacent_region : adjacent_regions) {
             adjacent_region->map(space().page_directory());
@@ -475,11 +479,15 @@ KResultOr<int> Process::sys$munmap(Userspace<void*> addr, size_t size)
         if (!old_region->is_mmap())
             return EPERM;
 
-        auto new_regions = space().split_region_around_range(*old_region, range_to_unmap);
+        // Remove the old region from our regions tree, since were going to add another region
+        // with the exact same start address, but dont deallocate it yet
+        auto region = space().take_region(*old_region);
+        VERIFY(region);
 
         // We manually unmap the old region here, specifying that we *don't* want the VM deallocated.
-        old_region->unmap(Region::ShouldDeallocateVirtualMemoryRange::No);
-        space().deallocate_region(*old_region);
+        region->unmap(Region::ShouldDeallocateVirtualMemoryRange::No);
+
+        auto new_regions = space().split_region_around_range(*region, range_to_unmap);
 
         // Instead we give back the unwanted VM manually.
         space().page_directory().range_allocator().deallocate(range_to_unmap);
@@ -512,13 +520,16 @@ KResultOr<int> Process::sys$munmap(Userspace<void*> addr, size_t size)
             continue;
         }
 
-        // otherwise just split the regions and collect them for future mapping
-        new_regions.append(space().split_region_around_range(*old_region, range_to_unmap));
+        // Remove the old region from our regions tree, since were going to add another region
+        // with the exact same start address, but dont deallocate it yet
+        auto region = space().take_region(*old_region);
+        VERIFY(region);
 
         // We manually unmap the old region here, specifying that we *don't* want the VM deallocated.
-        old_region->unmap(Region::ShouldDeallocateVirtualMemoryRange::No);
-        bool res = space().deallocate_region(*old_region);
-        VERIFY(res);
+        region->unmap(Region::ShouldDeallocateVirtualMemoryRange::No);
+
+        // otherwise just split the regions and collect them for future mapping
+        new_regions.append(space().split_region_around_range(*region, range_to_unmap));
     }
     // Instead we give back the unwanted VM manually at the end.
     space().page_directory().range_allocator().deallocate(range_to_unmap);
@@ -559,7 +570,8 @@ KResultOr<FlatPtr> Process::sys$mremap(Userspace<const Syscall::SC_mremap_params
 
         // Unmap without deallocating the VM range since we're going to reuse it.
         old_region->unmap(Region::ShouldDeallocateVirtualMemoryRange::No);
-        space().deallocate_region(*old_region);
+        bool success = space().deallocate_region(*old_region);
+        VERIFY(success);
 
         auto new_vmobject = PrivateInodeVMObject::create_with_inode(inode);
 
diff --git a/Kernel/VM/Space.cpp b/Kernel/VM/Space.cpp
index 94a7628f95..bb48d700d0 100644
--- a/Kernel/VM/Space.cpp
+++ b/Kernel/VM/Space.cpp
@@ -118,18 +118,21 @@ KResultOr<Region*> Space::allocate_region_with_vmobject(const Range& range, Nonn
 
 bool Space::deallocate_region(Region& region)
 {
-    OwnPtr<Region> region_protector;
+    return take_region(region);
+}
+
+OwnPtr<Region> Space::take_region(Region& region)
+{
     ScopedSpinLock lock(m_lock);
 
     if (m_region_lookup_cache.region.unsafe_ptr() == &region)
         m_region_lookup_cache.region = nullptr;
     for (size_t i = 0; i < m_regions.size(); ++i) {
         if (&m_regions[i] == &region) {
-            region_protector = m_regions.unstable_take(i);
-            return true;
+            return m_regions.unstable_take(i);
         }
     }
-    return false;
+    return {};
 }
 
 Region* Space::find_region_from_range(const Range& range)
diff --git a/Kernel/VM/Space.h b/Kernel/VM/Space.h
index dde64230dc..fd5ae428b1 100644
--- a/Kernel/VM/Space.h
+++ b/Kernel/VM/Space.h
@@ -58,6 +58,7 @@ public:
     KResultOr<Region*> allocate_region_with_vmobject(const Range&, NonnullRefPtr<VMObject>, size_t offset_in_vmobject, const String& name, int prot, bool shared);
     KResultOr<Region*> allocate_region(const Range&, const String& name, int prot = PROT_READ | PROT_WRITE, AllocationStrategy strategy = AllocationStrategy::Reserve);
     bool deallocate_region(Region& region);
+    OwnPtr<Region> take_region(Region& region);
 
     Region& allocate_split_region(const Region& source_region, const Range&, size_t offset_in_vmobject);
     Vector<Region*, 2> split_region_around_range(const Region& source_region, const Range&);