PCScan: Move bitmap committing into PCScan initialization

Scan should know what it needs for book keeping.

Bug: 11297512
Change-Id: Ie73d362a9632f5b5eb365c0ce1fba72c62887f44
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2541864Reviewed-by: Bartek Nowierski <bartekn@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828108}

base/allocator/partition_allocator/partition_root.h

@@ -303,27 +303,11 @@ struct BASE_EXPORT PartitionRoot {
 
   void EnablePCScan() {
     PA_CHECK(scannable && !pcscan.has_value());
-
-    {
-      // Setting |pcscan| and committing bitmaps has to be done under the lock
-      // to avoid racing with PartitionBucket::AllocNewSlotSpan.
-      internal::ScopedGuard<thread_safe> guard{lock_};
-
-      size_t quarantine_bitmaps_size_to_commit =
-          internal::CommittedQuarantineBitmapsSize();
-      for (auto* super_page_extent = first_extent; super_page_extent;
-           super_page_extent = super_page_extent->next) {
-        for (char* super_page = super_page_extent->super_page_base;
-             super_page != super_page_extent->super_pages_end;
-             super_page += kSuperPageSize) {
-          SetSystemPagesAccess(internal::SuperPageQuarantineBitmaps(super_page),
-                               quarantine_bitmaps_size_to_commit,
-                               PageReadWrite);
-        }
-      }
-
-      pcscan.emplace(this);
-    }
+    // Setting |pcscan| and committing bitmaps has to be done under the lock to
+    // avoid racing with PartitionBucket::AllocNewSlotSpan and avoid racing on
+    // |pcscan| ifself during free calls.
+    internal::ScopedGuard<thread_safe> guard{lock_};
+    pcscan.emplace(this);
   }
 
   static PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR ALWAYS_INLINE size_t

base/allocator/partition_allocator/pcscan.h

@@ -8,6 +8,7 @@
 #include <atomic>
 
 #include "base/allocator/partition_allocator/object_bitmap.h"
+#include "base/allocator/partition_allocator/page_allocator.h"
 #include "base/allocator/partition_allocator/partition_alloc_forward.h"
 #include "base/allocator/partition_allocator/partition_direct_map_extent.h"
 #include "base/allocator/partition_allocator/partition_page.h"
@@ -38,7 +39,7 @@ class BASE_EXPORT PCScan final {
   using Root = PartitionRoot<thread_safe>;
   using SlotSpan = SlotSpanMetadata<thread_safe>;
 
-  explicit PCScan(Root* root) : root_(root) {}
+  explicit PCScan(Root* root);
 
   PCScan(const PCScan&) = delete;
   PCScan& operator=(const PCScan&) = delete;
@@ -85,6 +86,22 @@ class BASE_EXPORT PCScan final {
 template <bool thread_safe>
 constexpr size_t PCScan<thread_safe>::QuarantineData::kQuarantineSizeMinLimit;
 
+template <bool thread_safe>
+PCScan<thread_safe>::PCScan(Root* root) : root_(root) {
+  root->lock_.AssertAcquired();
+  // Commit quarantine bitmaps.
+  size_t quarantine_bitmaps_size_to_commit = CommittedQuarantineBitmapsSize();
+  for (auto* super_page_extent = root->first_extent; super_page_extent;
+       super_page_extent = super_page_extent->next) {
+    for (char* super_page = super_page_extent->super_page_base;
+         super_page != super_page_extent->super_pages_end;
+         super_page += kSuperPageSize) {
+      SetSystemPagesAccess(internal::SuperPageQuarantineBitmaps(super_page),
+                           quarantine_bitmaps_size_to_commit, PageReadWrite);
+    }
+  }
+}
+
 template <bool thread_safe>
 bool PCScan<thread_safe>::QuarantineData::Account(size_t size) {
   size_t size_before = current_size_.fetch_add(size, std::memory_order_relaxed);