runtime: prevent garbage collection during hashmap insertion
Inserting a key-value pair into a hashmap storing keys or values
indirectly can cause the garbage collector to find the hashmap in
an inconsistent state.
Fixes #5074.
R=golang-dev, minux.ma, rsc
CC=golang-dev
https://golang.org/cl/7913043
diff --git a/src/pkg/runtime/gc_test.go b/src/pkg/runtime/gc_test.go
index e1e1b1d..3475339 100644
--- a/src/pkg/runtime/gc_test.go
+++ b/src/pkg/runtime/gc_test.go
@@ -7,6 +7,7 @@
import (
"os"
"runtime"
+ "runtime/debug"
"testing"
)
@@ -82,3 +83,17 @@
t.Fail()
}
}
+
+func TestGcHashmapIndirection(t *testing.T) {
+ defer debug.SetGCPercent(debug.SetGCPercent(1))
+ runtime.GC()
+ type T struct {
+ a [256]int
+ }
+ m := make(map[T]T)
+ for i := 0; i < 2000; i++ {
+ var a T
+ a.a[0] = i
+ m[a] = T{}
+ }
+}
diff --git a/src/pkg/runtime/hashmap.c b/src/pkg/runtime/hashmap.c
index 37111da..dc5dfb8 100644
--- a/src/pkg/runtime/hashmap.c
+++ b/src/pkg/runtime/hashmap.c
@@ -1016,10 +1016,12 @@
res = nil;
hit = hash_insert(t, h, ak, (void**)&res);
if(!hit) {
+ // Need to pass dogc=0 to runtime·mallocgc because the garbage collector
+ // is assuming that all hashmaps are in a consistent state.
if(h->flag & IndirectKey)
- *(void**)res = runtime·mal(t->key->size);
+ *(void**)res = runtime·mallocgc(t->key->size, 0, 0, 1);
if(h->flag & IndirectVal)
- *(void**)(res+h->valoff) = runtime·mal(t->elem->size);
+ *(void**)(res+h->valoff) = runtime·mallocgc(t->elem->size, 0, 0, 1);
}
t->key->alg->copy(t->key->size, hash_keyptr(h, res), ak);
t->elem->alg->copy(t->elem->size, hash_valptr(h, res), av);
diff --git a/src/pkg/runtime/mgc0.c b/src/pkg/runtime/mgc0.c
index ce36293..a79c22e 100644
--- a/src/pkg/runtime/mgc0.c
+++ b/src/pkg/runtime/mgc0.c
@@ -932,14 +932,26 @@
if(!(mapkey_kind & KindNoPointers) || d.indirectkey) {
if(!d.indirectkey)
*objbufpos++ = (Obj){d.key_data, mapkey_size, mapkey_ti};
- else
+ else {
+ if(Debug) {
+ obj = *(void**)d.key_data;
+ if(!(arena_start <= obj && obj < arena_used))
+ runtime·throw("scanblock: inconsistent hashmap");
+ }
*ptrbufpos++ = (PtrTarget){*(void**)d.key_data, mapkey_ti};
+ }
}
if(!(mapval_kind & KindNoPointers) || d.indirectval) {
if(!d.indirectval)
*objbufpos++ = (Obj){d.val_data, mapval_size, mapval_ti};
- else
+ else {
+ if(Debug) {
+ obj = *(void**)d.val_data;
+ if(!(arena_start <= obj && obj < arena_used))
+ runtime·throw("scanblock: inconsistent hashmap");
+ }
*ptrbufpos++ = (PtrTarget){*(void**)d.val_data, mapval_ti};
+ }
}
}
}
