From 43f5f33913d03de4d9602b7e07b0b0666f564e98 Mon Sep 17 00:00:00 2001
From: Matthew Parkinson <mattpark@microsoft.com>
Date: Mon, 11 Apr 2022 11:38:43 +0100
Subject: [PATCH] Fix missing consolidation marker

During creation of large allocation the code was not setting the
consolidation bit. This meant that Windows would crash for certain patterns for large
allocations.
---
 src/snmalloc/backend/backend.h                | 14 +++++------
 .../backend_helpers/largebuddyrange.h         | 23 ++-----------------
 .../backend_helpers/pagemapregisterrange.h    | 10 +++++++-
 src/snmalloc/mem/metadata.h                   |  3 ++-
 4 files changed, 19 insertions(+), 31 deletions(-)

diff --git a/src/snmalloc/backend/backend.h b/src/snmalloc/backend/backend.h
index cbff62b..d9a2d23 100644
--- a/src/snmalloc/backend/backend.h
+++ b/src/snmalloc/backend/backend.h
@@ -108,15 +108,13 @@ namespace snmalloc
 #else
     // Set up source of memory
     using P = PalRange<DefaultPal>;
-    using Base = std::
-      conditional_t<fixed_range, EmptyRange, PagemapRegisterRange<Pagemap, P>>;
+    using Base = std::conditional_t<
+      fixed_range,
+      EmptyRange,
+      PagemapRegisterRange<Pagemap, P, CONSOLIDATE_PAL_ALLOCS>>;
     // Global range of memory
-    using StatsR = StatsRange<LargeBuddyRange<
-      Base,
-      24,
-      bits::BITS - 1,
-      Pagemap,
-      CONSOLIDATE_PAL_ALLOCS>>;
+    using StatsR =
+      StatsRange<LargeBuddyRange<Base, 24, bits::BITS - 1, Pagemap>>;
     using GlobalR = GlobalRange<StatsR>;
 
 #  ifdef SNMALLOC_META_PROTECTED
diff --git a/src/snmalloc/backend_helpers/largebuddyrange.h b/src/snmalloc/backend_helpers/largebuddyrange.h
index 3248df1..6a7bd24 100644
--- a/src/snmalloc/backend_helpers/largebuddyrange.h
+++ b/src/snmalloc/backend_helpers/largebuddyrange.h
@@ -169,8 +169,7 @@ namespace snmalloc
     typename ParentRange,
     size_t REFILL_SIZE_BITS,
     size_t MAX_SIZE_BITS,
-    SNMALLOC_CONCEPT(ConceptBuddyRangeMeta) Pagemap,
-    bool Consolidate = true>
+    SNMALLOC_CONCEPT(ConceptBuddyRangeMeta) Pagemap>
   class LargeBuddyRange
   {
     ParentRange parent{};
@@ -218,24 +217,7 @@ namespace snmalloc
     void add_range(capptr::Chunk<void> base, size_t length)
     {
       range_to_pow_2_blocks<MIN_CHUNK_BITS>(
-        base,
-        length,
-        [this](capptr::Chunk<void> base, size_t align, bool first) {
-          if constexpr (!Consolidate)
-          {
-            // Tag first entry so we don't consolidate it.
-            if (first)
-            {
-              auto& entry = Pagemap::get_metaentry_mut(address_cast(base));
-              entry.claim_for_backend();
-              entry.set_boundary();
-            }
-          }
-          else
-          {
-            UNUSED(first);
-          }
-
+        base, length, [this](capptr::Chunk<void> base, size_t align, bool) {
           auto overflow = capptr::Chunk<void>(reinterpret_cast<void*>(
             buddy_large.add_block(base.unsafe_uintptr(), align)));
 
@@ -247,7 +229,6 @@ namespace snmalloc
     {
       if (ParentRange::Aligned)
       {
-        // TODO have to add consolidation blocker for these cases.
         if (size >= REFILL_SIZE)
         {
           return parent.alloc_range(size);
diff --git a/src/snmalloc/backend_helpers/pagemapregisterrange.h b/src/snmalloc/backend_helpers/pagemapregisterrange.h
index 17ba6e1..de60dd8 100644
--- a/src/snmalloc/backend_helpers/pagemapregisterrange.h
+++ b/src/snmalloc/backend_helpers/pagemapregisterrange.h
@@ -6,7 +6,8 @@ namespace snmalloc
 {
   template<
     SNMALLOC_CONCEPT(ConceptBackendMetaRange) Pagemap,
-    typename ParentRange>
+    typename ParentRange,
+    bool CanConsolidate = true>
   class PagemapRegisterRange
   {
     ParentRange state{};
@@ -25,6 +26,13 @@ namespace snmalloc
       if (base != nullptr)
         Pagemap::register_range(address_cast(base), size);
 
+      if (!CanConsolidate)
+      {
+        // Mark start of allocation in pagemap.
+        auto& entry = Pagemap::get_metaentry_mut(address_cast(base));
+        entry.set_boundary();
+      }
+
       return base;
     }
   };
diff --git a/src/snmalloc/mem/metadata.h b/src/snmalloc/mem/metadata.h
index ac56f0a..ca90ec1 100644
--- a/src/snmalloc/mem/metadata.h
+++ b/src/snmalloc/mem/metadata.h
@@ -129,7 +129,8 @@ namespace snmalloc
      */
     [[nodiscard]] bool is_unowned() const
     {
-      return (meta == 0) && (remote_and_sizeclass == 0);
+      return ((meta == 0) || (meta == META_BOUNDARY_BIT)) &&
+        (remote_and_sizeclass == 0);
     }
 
     /**