runtime: disable scavenger on 64k page size kernels

Update #9993

If the physical page size of the machine is larger than the logical
heap size, for example 8k logical, 64k physical, then madvise(2) will
round up the requested amount to a 64k boundary and may discard pages
close to the page being madvised.

This patch disables the scavenger in these situations, which at the moment
is only ppc64 and ppc64le systems. NaCl also uses a 64k page size, but
it's not clear if it is affected by this problem.

Change-Id: Ib897f8d3df5bd915ddc0b510f2fd90a30ef329ca
Reviewed-on: https://go-review.googlesource.com/6091
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

diff --git a/src/runtime/debug/garbage_test.go b/src/runtime/debug/garbage_test.go
index 54c33bd4f3f4e48da2fa8a64051741fc04fdbb5f..a392614b1f6eacfb251ccaf6387caf85f14892ad 100644 (file)
--- a/src/runtime/debug/garbage_test.go
+++ b/src/runtime/debug/garbage_test.go
@@ -88,6 +88,10 @@ func TestReadGCStats(t *testing.T) {
 var big = make([]byte, 1<<20)
 
 func TestFreeOSMemory(t *testing.T) {
+       switch runtime.GOARCH {
+       case "ppc64", "ppc64le", "nacl":
+               t.Skip("issue 9993; scavenger temporarily disabled on systems with 64k pages")
+       }
        var ms1, ms2 runtime.MemStats
 
        if big == nil {

diff --git a/src/runtime/mheap.go b/src/runtime/mheap.go
index a05a570ff1be71c411cfe02d01ba104377d66745..94ef4de56aae74eb7ed1adabb82a8afe54750518 100644 (file)
--- a/src/runtime/mheap.go
+++ b/src/runtime/mheap.go
@@ -717,6 +717,15 @@ func mHeap_FreeSpanLocked(h *mheap, s *mspan, acctinuse, acctidle bool, unusedsi
 }
 
 func scavengelist(list *mspan, now, limit uint64) uintptr {
+       if _PhysPageSize > _PageSize {
+               // golang.org/issue/9993
+               // If the physical page size of the machine is larger than
+               // our logical heap page size the kernel may round up the
+               // amount to be freed to its page size and corrupt the heap
+               // pages surrounding the unused block.
+               return 0
+       }
+
        if mSpanList_IsEmpty(list) {
                return 0
        }