absl: fix Mutex TSan annotations

TSan misses synchronization around passing PerThreadSynch between threads
since it happens inside of the Mutex code (which me mostly ignore),
so we need to ignore all accesses to the object.

PiperOrigin-RevId: 491297912
Change-Id: I13ea2015dee5c1a3fc4315c85112902ccffccc45

absl/synchronization/mutex.cc

@@ -591,10 +591,15 @@ static SynchLocksHeld *Synch_GetAllLocks() {
 void Mutex::IncrementSynchSem(Mutex *mu, PerThreadSynch *w) {
   if (mu) {
     ABSL_TSAN_MUTEX_PRE_DIVERT(mu, 0);
-  }
-  PerThreadSem::Post(w->thread_identity());
-  if (mu) {
+    // We miss synchronization around passing PerThreadSynch between threads
+    // since it happens inside of the Mutex code, so we need to ignore all
+    // accesses to the object.
+    ABSL_ANNOTATE_IGNORE_READS_AND_WRITES_BEGIN();
+    PerThreadSem::Post(w->thread_identity());
+    ABSL_ANNOTATE_IGNORE_READS_AND_WRITES_END();
     ABSL_TSAN_MUTEX_POST_DIVERT(mu, 0);
+  } else {
+    PerThreadSem::Post(w->thread_identity());
   }
 }