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runtime: ensure finalizers are zero-initialized before reuse 

We reuse finalizers in finblocks, which are allocated off-heap. This
means they have to be zero-initialized before becoming visible to the
garbage collector. We actually already do this by clearing the
finalizer before returning it to the pool, but we're not careful to
enforce correct memory ordering. Fix this by manipulating the
finalizer count atomically so these writes synchronize properly with
the garbage collector.

Updates #17503.

Change-Id: I7797d31df3c656c9fe654bc6da287f66a9e2037d
Reviewed-on: https://go-review.googlesource.com/31454
Reviewed-by: Rick Hudson <rlh@golang.org>
This commit is contained in:
Austin Clements 2016-10-14 13:39:07 -04:00
parent db56a63547
commit d3836aba31
2 changed files with 11 additions and 7 deletions
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15
src/runtime/mfinal.go
View File

@ -19,7 +19,7 @@ import (
type finblock struct {
alllink *finblock
next *finblock
cnt int32
cnt uint32
_ int32
fin [(_FinBlockSize - 2*sys.PtrSize - 2*4) / unsafe.Sizeof(finalizer{})]finalizer
}
@ -72,7 +72,7 @@ var finalizer1 = [...]byte{
func queuefinalizer(p unsafe.Pointer, fn *funcval, nret uintptr, fint *_type, ot *ptrtype) {
lock(&finlock)
if finq == nil || finq.cnt == int32(len(finq.fin)) {
if finq == nil || finq.cnt == uint32(len(finq.fin)) {
if finc == nil {
finc = (*finblock)(persistentalloc(_FinBlockSize, 0, &memstats.gc_sys))
finc.alllink = allfin
@ -99,7 +99,7 @@ func queuefinalizer(p unsafe.Pointer, fn *funcval, nret uintptr, fint *_type, ot
finq = block
}
f := &finq.fin[finq.cnt]
finq.cnt++
atomic.Xadd(&finq.cnt, +1) // Sync with markroots
f.fn = fn
f.nret = nret
f.fint = fint
@ -112,7 +112,7 @@ func queuefinalizer(p unsafe.Pointer, fn *funcval, nret uintptr, fint *_type, ot
//go:nowritebarrier
func iterate_finq(callback func(*funcval, unsafe.Pointer, uintptr, *_type, *ptrtype)) {
for fb := allfin; fb != nil; fb = fb.alllink {
for i := int32(0); i < fb.cnt; i++ {
for i := uint32(0); i < fb.cnt; i++ {
f := &fb.fin[i]
callback(f.fn, f.arg, f.nret, f.fint, f.ot)
}
@ -208,11 +208,14 @@ func runfinq() {
reflectcall(nil, unsafe.Pointer(f.fn), frame, uint32(framesz), uint32(framesz))
fingRunning = false
// drop finalizer queue references to finalized object
// Drop finalizer queue heap references
// before hiding them from markroot.
// This also ensures these will be
// clear if we reuse the finalizer.
f.fn = nil
f.arg = nil
f.ot = nil
fb.cnt = i - 1
atomic.Store(&fb.cnt, i-1)
}
next := fb.next
lock(&finlock)

3
src/runtime/mgcmark.go
View File

@ -186,7 +186,8 @@ func markroot(gcw *gcWork, i uint32) {
case i == fixedRootFinalizers:
for fb := allfin; fb != nil; fb = fb.alllink {
scanblock(uintptr(unsafe.Pointer(&fb.fin[0])), uintptr(fb.cnt)*unsafe.Sizeof(fb.fin[0]), &finptrmask[0], gcw)
cnt := uintptr(atomic.Load(&fb.cnt))
scanblock(uintptr(unsafe.Pointer(&fb.fin[0])), cnt*unsafe.Sizeof(fb.fin[0]), &finptrmask[0], gcw)
}
case i == fixedRootFreeGStacks: