Reland [Memory] Speculative fix for sanitizer flakiness.

- Uses a mutex to prevent races on getting random mmap addresses, on
  POSIX and Windows.

Original change's description:
> [Memory] Speculative fix for sanitizer flakiness.
>
> - When allocating virtual memory, make sure addresses don't interfere
>   with hard-coded sanitizer regions.
>
> Bug: v8:7146
> Change-Id: I5bcb664b32bf53c8581772fe329190da6033701f
> Reviewed-on: https://chromium-review.googlesource.com/833171
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Reviewed-by: Hannes Payer <hpayer@chromium.org>
> Commit-Queue: Bill Budge <bbudge@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50208}

Bug: v8:7146
Change-Id: I5a82f2a1f6136498fb2aa7a37e0206c506545073
Reviewed-on: https://chromium-review.googlesource.com/834453Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50216}

src/base/platform/platform-posix.cc

@@ -89,6 +89,7 @@ const char* g_gc_fake_mmap = nullptr;
 
 static LazyInstance<RandomNumberGenerator>::type
     platform_random_number_generator = LAZY_INSTANCE_INITIALIZER;
+static LazyMutex rng_mutex = LAZY_MUTEX_INITIALIZER;
 
 #if !V8_OS_FUCHSIA
 #if V8_OS_MACOSX
@@ -206,14 +207,21 @@ size_t OS::CommitPageSize() {
 
 // static
 void* OS::GetRandomMmapAddr() {
-#if defined(ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER) || \
-    defined(THREAD_SANITIZER)
-  // Dynamic tools do not support custom mmap addresses.
-  return nullptr;
-#else
   uintptr_t raw_addr;
+  {
+    LockGuard<Mutex> guard(rng_mutex.Pointer());
     platform_random_number_generator.Pointer()->NextBytes(&raw_addr,
                                                           sizeof(raw_addr));
+  }
+#if defined(V8_USE_ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER) || \
+    defined(THREAD_SANITIZER) || defined(LEAK_SANITIZER)
+  // If random hint addresses interfere with address ranges hard coded in
+  // sanitizers, bad things happen. This address range is copied from TSAN
+  // source but works with all tools.
+  // See crbug.com/539863.
+  raw_addr &= 0x007fffff0000ULL;
+  raw_addr += 0x7e8000000000ULL;
+#else
 #if V8_TARGET_ARCH_X64
   // Currently available CPUs have 48 bits of virtual addressing.  Truncate
   // the hint address to 46 bits to give the kernel a fighting chance of
@@ -267,8 +275,8 @@ void* OS::GetRandomMmapAddr() {
   raw_addr += 0x20000000;
 #endif
 #endif
-  return reinterpret_cast<void*>(raw_addr);
 #endif
+  return reinterpret_cast<void*>(raw_addr);
 }
 
 // TODO(bbudge) Move Cygwin and Fuschia stuff into platform-specific files.

src/base/platform/platform-win32.cc

@@ -699,6 +699,7 @@ size_t OS::CommitPageSize() {
 
 static LazyInstance<RandomNumberGenerator>::type
     platform_random_number_generator = LAZY_INSTANCE_INITIALIZER;
+static LazyMutex rng_mutex = LAZY_MUTEX_INITIALIZER;
 
 void OS::Initialize(int64_t random_seed, bool hard_abort,
                     const char* const gc_fake_mmap) {
@@ -722,8 +723,11 @@ void* OS::GetRandomMmapAddr() {
   static const uintptr_t kAllocationRandomAddressMax = 0x3FFF0000;
 #endif
   uintptr_t address;
+  {
+    LockGuard<Mutex> guard(rng_mutex.Pointer());
     platform_random_number_generator.Pointer()->NextBytes(&address,
                                                           sizeof(address));
+  }
   address <<= kPageSizeBits;
   address += kAllocationRandomAddressMin;
   address &= kAllocationRandomAddressMax;