runtime: avoid stat underflow crash
If the area returned by sysReserve in mheap.sysAlloc is outside the
usable arena, we sysFree it. We pass a fake stat pointer to sysFree
because we haven't added the allocation to any stat at that point.
However, we pass a 0 stat, so sysFree panics when it decrements the
stat because the fake stat underflows.
Fix this by setting the fake stat to the allocation size.
Updates #13143 (this is a prerequisite to fixing that bug).
Change-Id: I61a6c9be19ac1c95863cf6a8435e19790c8bfc9a
Reviewed-on: https://go-review.googlesource.com/16926
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go
index 6430511..8ce420a 100644
--- a/src/runtime/malloc.go
+++ b/src/runtime/malloc.go
@@ -414,7 +414,10 @@
h.arena_used = used
h.arena_reserved = reserved
} else {
- var stat uint64
+ // We haven't added this allocation to
+ // the stats, so subtract it from a
+ // fake stat (but avoid underflow).
+ stat := uint64(p_size)
sysFree(unsafe.Pointer(p), p_size, &stat)
}
}
