Rework selection of error type to avoid spin lock.

- Remove storage of write_flag from GuardedPageAllocator::SlotMetadata.
- Remove method GuardedPageAllocator::SetWriteFlag
- Remove refining the return value of GetErrorType (as write_flag is no
  longer present)
- Add refining the error value to the SegVHandler.

PiperOrigin-RevId: 573306812
Change-Id: I75d90ac2daeb18a5375dd172b4242bb90d39fcba

tcmalloc/guarded_page_allocator.cc

@@ -111,7 +111,6 @@ GuardedAllocWithStatus GuardedPageAllocator::Allocate(size_t size,
   d.alloc_trace.tid = absl::base_internal::GetTID();
   d.requested_size = size;
   d.allocation_start = reinterpret_cast<uintptr_t>(result);
-  d.write_flag = WriteFlag::Unknown;
 
   ASSERT(!alignment || d.allocation_start % alignment == 0);
   return {result, Profile::Sample::GuardedStatus::Guarded};
@@ -245,13 +244,6 @@ size_t GuardedPageAllocator::SuccessfulAllocations() {
   return num_allocation_requests_ - num_failed_allocations_;
 }
 
-void GuardedPageAllocator::SetWriteFlag(const void* ptr, WriteFlag write_flag) {
-  const uintptr_t addr = reinterpret_cast<uintptr_t>(ptr);
-  size_t slot = GetNearestSlot(addr);
-  absl::base_internal::SpinLockHolder h(&guarded_page_lock_);
-  data_[slot].write_flag = write_flag;
-}
-
 // Maps 2 * total_pages_ + 1 pages so that there are total_pages_ unique pages
 // we can return from Allocate with guard pages before and after them.
 void GuardedPageAllocator::MapPages() {
@@ -377,34 +369,13 @@ GuardedAllocationsErrorType GuardedPageAllocator::GetErrorType(
   if (write_overflow_detected_)
     return GuardedAllocationsErrorType::kBufferOverflowOnDealloc;
   if (d.dealloc_trace.depth > 0) {
-    switch (d.write_flag) {
-      case WriteFlag::Write:
-        return GuardedAllocationsErrorType::kUseAfterFreeWrite;
-      case WriteFlag::Read:
-        return GuardedAllocationsErrorType::kUseAfterFreeRead;
-      default:
-        return GuardedAllocationsErrorType::kUseAfterFree;
-    }
+    return GuardedAllocationsErrorType::kUseAfterFree;
   }
   if (addr < d.allocation_start) {
-    switch (d.write_flag) {
-      case WriteFlag::Write:
-        return GuardedAllocationsErrorType::kBufferUnderflowWrite;
-      case WriteFlag::Read:
-        return GuardedAllocationsErrorType::kBufferUnderflowRead;
-      default:
-        return GuardedAllocationsErrorType::kBufferUnderflow;
-    }
+    return GuardedAllocationsErrorType::kBufferUnderflow;
   }
   if (addr >= d.allocation_start + d.requested_size) {
-    switch (d.write_flag) {
-      case WriteFlag::Write:
-        return GuardedAllocationsErrorType::kBufferOverflowWrite;
-      case WriteFlag::Read:
-        return GuardedAllocationsErrorType::kBufferOverflowRead;
-      default:
-        return GuardedAllocationsErrorType::kBufferOverflow;
-    }
+    return GuardedAllocationsErrorType::kBufferOverflow;
   }
   return GuardedAllocationsErrorType::kUnknown;
 }

tcmalloc/guarded_page_allocator.h

@@ -173,9 +173,6 @@ class GuardedPageAllocator {
 
   size_t SuccessfulAllocations() ABSL_LOCKS_EXCLUDED(guarded_page_lock_);
 
-  void SetWriteFlag(const void* ptr, WriteFlag write_flag)
-      ABSL_LOCKS_EXCLUDED(guarded_page_lock_);
-
   size_t page_size() const { return page_size_; }
 
  private:
@@ -185,7 +182,6 @@ class GuardedPageAllocator {
     GuardedAllocationsStackTrace dealloc_trace;
     size_t requested_size = 0;
     uintptr_t allocation_start = 0;
-    WriteFlag write_flag = WriteFlag::Unknown;
   };
 
   // Max number of magic bytes we use to detect write-overflows at deallocation.

tcmalloc/segv_handler.cc

@@ -151,6 +151,45 @@ static WriteFlag ExtractWriteFlagFromContext(void* context) {
 #endif
 }
 
+GuardedAllocationsErrorType RefineErrorTypeBasedOnWriteFlag(
+    GuardedAllocationsErrorType error, WriteFlag write_flag) {
+  switch (error) {
+    case GuardedAllocationsErrorType::kUseAfterFree:
+      switch (write_flag) {
+        case WriteFlag::Write:
+          return GuardedAllocationsErrorType::kUseAfterFreeWrite;
+        case WriteFlag::Read:
+          return GuardedAllocationsErrorType::kUseAfterFreeRead;
+        default:
+          break;
+      }
+      break;
+    case GuardedAllocationsErrorType::kBufferUnderflow:
+      switch (write_flag) {
+        case WriteFlag::Write:
+          return GuardedAllocationsErrorType::kBufferUnderflowWrite;
+        case WriteFlag::Read:
+          return GuardedAllocationsErrorType::kBufferUnderflowRead;
+        default:
+          break;
+      }
+      break;
+    case GuardedAllocationsErrorType::kBufferOverflow:
+      switch (write_flag) {
+        case WriteFlag::Write:
+          return GuardedAllocationsErrorType::kBufferOverflowWrite;
+        case WriteFlag::Read:
+          return GuardedAllocationsErrorType::kBufferOverflowRead;
+        default:
+          break;
+      }
+      break;
+    default:
+      break;
+  }
+  return error;
+}
+
 // A SEGV handler that prints stack traces for the allocation and deallocation
 // of relevant memory as well as the location of the memory error.
 void SegvHandler(int signo, siginfo_t* info, void* context) {
@@ -160,13 +199,13 @@ void SegvHandler(int signo, siginfo_t* info, void* context) {
 
   // Store load/store from context.
   WriteFlag write_flag = ExtractWriteFlagFromContext(context);
-  tc_globals.guardedpage_allocator().SetWriteFlag(fault, write_flag);
 
   GuardedAllocationsStackTrace *alloc_trace, *dealloc_trace;
   GuardedAllocationsErrorType error =
       tc_globals.guardedpage_allocator().GetStackTraces(fault, &alloc_trace,
                                                         &dealloc_trace);
   if (error == GuardedAllocationsErrorType::kUnknown) return;
+  error = RefineErrorTypeBasedOnWriteFlag(error, write_flag);
   pid_t current_thread = absl::base_internal::GetTID();
   off_t offset;
   size_t size;