From 0f3bb466b868b523cf1dc9b2aaaed65c77b28862 Mon Sep 17 00:00:00 2001
From: Derek Mauro <761129+derekmauro@users.noreply.github.com>
Date: Wed, 21 Oct 2020 08:32:42 -0400
Subject: Cherry-picks for LTS 2020_09_23 Patch Release 2

* Fixes preprocessor condition for symbols __tsan_mutex_read_lock and
__tsan_mutex_try_lock
* Fixes race in AddressIsReadable file descriptors using stronger memory ordering
* Fixes CMake dependency issues and adds `-Wl,--no-undefined` to avoid
these issues in the future.
---
 absl/debugging/internal/address_is_readable.cc | 9 +++++----
 absl/flags/CMakeLists.txt                      | 1 +
 absl/status/CMakeLists.txt                     | 1 +
 absl/synchronization/mutex.cc                  | 5 +++--
 4 files changed, 10 insertions(+), 6 deletions(-)

(limited to 'absl')

diff --git a/absl/debugging/internal/address_is_readable.cc b/absl/debugging/internal/address_is_readable.cc
index 65376063..329c285f 100644
--- a/absl/debugging/internal/address_is_readable.cc
+++ b/absl/debugging/internal/address_is_readable.cc
@@ -68,6 +68,7 @@ static void Unpack(uint64_t x, int *pid, int *read_fd, int *write_fd) {
 // unimplemented.
 // This is a namespace-scoped variable for correct zero-initialization.
 static std::atomic<uint64_t> pid_and_fds;  // initially 0, an invalid pid.
+
 bool AddressIsReadable(const void *addr) {
   absl::base_internal::ErrnoSaver errno_saver;
   // We test whether a byte is readable by using write().  Normally, this would
@@ -86,7 +87,7 @@ bool AddressIsReadable(const void *addr) {
     int pid;
     int read_fd;
     int write_fd;
-    uint64_t local_pid_and_fds = pid_and_fds.load(std::memory_order_relaxed);
+    uint64_t local_pid_and_fds = pid_and_fds.load(std::memory_order_acquire);
     Unpack(local_pid_and_fds, &pid, &read_fd, &write_fd);
     while (current_pid != pid) {
       int p[2];
@@ -98,13 +99,13 @@ bool AddressIsReadable(const void *addr) {
       fcntl(p[1], F_SETFD, FD_CLOEXEC);
       uint64_t new_pid_and_fds = Pack(current_pid, p[0], p[1]);
       if (pid_and_fds.compare_exchange_strong(
-              local_pid_and_fds, new_pid_and_fds, std::memory_order_relaxed,
+              local_pid_and_fds, new_pid_and_fds, std::memory_order_release,
               std::memory_order_relaxed)) {
         local_pid_and_fds = new_pid_and_fds;  // fds exposed to other threads
       } else {  // fds not exposed to other threads; we can close them.
         close(p[0]);
         close(p[1]);
-        local_pid_and_fds = pid_and_fds.load(std::memory_order_relaxed);
+        local_pid_and_fds = pid_and_fds.load(std::memory_order_acquire);
       }
       Unpack(local_pid_and_fds, &pid, &read_fd, &write_fd);
     }
@@ -124,7 +125,7 @@ bool AddressIsReadable(const void *addr) {
       // If pid_and_fds contains the problematic file descriptors we just used,
       // this call will forget them, and the loop will try again.
       pid_and_fds.compare_exchange_strong(local_pid_and_fds, 0,
-                                          std::memory_order_relaxed,
+                                          std::memory_order_release,
                                           std::memory_order_relaxed);
     }
   } while (errno == EBADF);
diff --git a/absl/flags/CMakeLists.txt b/absl/flags/CMakeLists.txt
index 28bd5a85..88551914 100644
--- a/absl/flags/CMakeLists.txt
+++ b/absl/flags/CMakeLists.txt
@@ -183,6 +183,7 @@ absl_cc_library(
   DEPS
     absl::base
     absl::config
+    absl::flags_commandlineflag
     absl::flags_commandlineflag_internal
     absl::flags_config
     absl::flags_marshalling
diff --git a/absl/status/CMakeLists.txt b/absl/status/CMakeLists.txt
index 66728551..f0d798a3 100644
--- a/absl/status/CMakeLists.txt
+++ b/absl/status/CMakeLists.txt
@@ -64,6 +64,7 @@ absl_cc_library(
   COPTS
     ${ABSL_DEFAULT_COPTS}
   DEPS
+    absl::status
     absl::core_headers
     absl::raw_logging_internal
     absl::type_traits
diff --git a/absl/synchronization/mutex.cc b/absl/synchronization/mutex.cc
index 9b7f088a..ad13567a 100644
--- a/absl/synchronization/mutex.cc
+++ b/absl/synchronization/mutex.cc
@@ -50,6 +50,7 @@
 #include "absl/base/internal/spinlock.h"
 #include "absl/base/internal/sysinfo.h"
 #include "absl/base/internal/thread_identity.h"
+#include "absl/base/internal/tsan_mutex_interface.h"
 #include "absl/base/port.h"
 #include "absl/debugging/stacktrace.h"
 #include "absl/debugging/symbolize.h"
@@ -705,7 +706,7 @@ static constexpr bool kDebugMode = false;
 static constexpr bool kDebugMode = true;
 #endif
 
-#ifdef ABSL_HAVE_THREAD_SANITIZER
+#ifdef ABSL_INTERNAL_HAVE_TSAN_INTERFACE
 static unsigned TsanFlags(Mutex::MuHow how) {
   return how == kShared ? __tsan_mutex_read_lock : 0;
 }
@@ -1767,7 +1768,7 @@ static inline bool EvalConditionAnnotated(const Condition *cond, Mutex *mu,
   // All memory accesses are ignored inside of mutex operations + for unlock
   // operation tsan considers that we've already released the mutex.
   bool res = false;
-#ifdef ABSL_HAVE_THREAD_SANITIZER
+#ifdef ABSL_INTERNAL_HAVE_TSAN_INTERFACE
   const int flags = read_lock ? __tsan_mutex_read_lock : 0;
   const int tryflags = flags | (trylock ? __tsan_mutex_try_lock : 0);
 #endif
-- 
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