On deallocation overflow, use the virtual CPU ID if present.

When using a virtual CPU IDs, __rseq_abi.cpu_id corresponds to a different ID.
The overflow path will attempt to grow the cache on the real CPU ID slab, but
subsequent deallocations still using the virtual CPU ID will continue to
overflow.

PiperOrigin-RevId: 318500444
Change-Id: Iabb719be0ffed9acce88c2b592a59c2d7d7e27ef

Author: ckennelly

tcmalloc/internal/percpu_tcmalloc.h

@@ -347,7 +347,7 @@ static inline ABSL_ATTRIBUTE_ALWAYS_INLINE int TcmallocSlab_Push(
   // As of 3/2020, LLVM's asm goto (even with output constraints) only provides
   // values for the fallthrough path.  The values on the taken branches are
   // undefined.
-  int cpu = __rseq_abi.cpu_id;
+  int cpu = VirtualRseqCpuId();
   return f(cpu, cl, item);
 }
 #endif  // defined(__x86_64__)

tcmalloc/internal/percpu_tcmalloc_test.cc

@@ -295,7 +295,8 @@ TEST_P(TcmallocSlabTest, Unit) {
     __rseq_abi.cpu_id = cpu;
 
     if (UsingFlatVirtualCpus()) {
-      __rseq_abi.vcpu_id = cpu;
+      __rseq_abi.vcpu_id = cpu ^ 1;
+      cpu = cpu ^ 1;
     }
 #endif
     current_cpu_ = cpu;