Avoid reentrancy of the same thread in AbslFailureSignalHandler()

PiperOrigin-RevId: 947787991
Change-Id: Ic5f07a6f76e28545d61535c9215462bfd57c355c

Author: Abseil Team

absl/debugging/failure_signal_handler.cc

@@ -383,10 +383,16 @@ static void AbslFailureSignalHandler(int signo, siginfo_t*, void* ucontext) {
       // a bit for it to finish. If the other thread doesn't kill us,
       // we do so after sleeping.
       PortableSleepForSeconds(3);
-      RaiseToDefaultHandler(signo);
-      // The recursively raised signal may be blocked until we return.
-      return;
+    } else {
+      // Same thread re-entered: the handler itself faulted. Do NOT fall through
+      // and re-run the body (which would recurse under SA_NODEFER, resetting
+      // the alarm each time and consuming the unguarded altstack). Instead,
+      // terminate now.
     }
+
+    RaiseToDefaultHandler(signo);
+    // The recursively raised signal may be blocked until we return.
+    return;
   }
 
   // Increase the chance that the CPU we report was the same CPU on which the