@@ -98,8 +98,12 @@ func (xctn *Base) Bck() *meta.Bck { return &xctn.bck }
 // return true if 'stopping' OR 'finished'
 func (xctn *Base) IsDone() bool { return xctn.eutime.Load() != 0 }
 
-// mark the xaction as stopping (and finishing soon); EndTime remains zero until Finish()
-func (xctn *Base) SetStopping() { xctn.eutime.CAS(0, cos.MSB64) } // i.e., not running vis-à-vis xreg
+// mark the xaction as stopping (and finishing soon);
+// callers that perform terminal cleanup can use the return value to decide
+// whether they own that cleanup path
+func (xctn *Base) SetStopping() bool {
+	return xctn.eutime.CAS(0, cos.MSB64)
+}
 
 func (xctn *Base) IsRunning() (yes bool) {
 	yes = xctn.sutime.Load() != 0 && !xctn.IsDone() && !xctn.IsAborted()
 
@@ -43,7 +43,8 @@ type (
 			d    atomic.Int64 // duration hk idle
 			last atomic.Int64 // mono.NanoTime
 		}
-		pending atomic.Int64
+		pending  atomic.Int64
+		unregged atomic.Bool // hk.Unreg() at most once per instance; NOTE: same-UUID renewals reuse HK names
 	}
 )
 
@@ -76,7 +77,9 @@ func (r *DemandBase) Init(uuid, kind string, bck *meta.Bck, idleDur time.Duratio
 	r.InitBase(uuid, kind, bck)
 
 	r.idle.last.Store(mono.NanoTime())
+
 	hk.Reg(r.hkName+hk.NameSuffix, r.hkcb, 0 /*time.Duration*/)
+	r.unregged.Store(false)
 }
 
 // (e.g. usage: listed last page)
@@ -124,14 +127,19 @@ func (r *DemandBase) SubPending(n int) {
 }
 
 func (r *DemandBase) Stop() {
+	if !r.unregged.CAS(false, true) {
+		return
+	}
 	r.SetStopping()
 	hk.Unreg(r.hkName + hk.NameSuffix)
 	if r.ticks != nil {
 		r.ticks.Close()
-		r.ticks = nil
 	}
 }
 
+// Only abort the Base part, and note:
+// for demand xactions, Stop() is a cleanup-sequence sensitive barrier: it unregisters
+// the idle HK callback and can allow same-UUID renewal to register the same HK name.
 func (r *DemandBase) Abort(err error) (ok bool) {
 	if err == nil && !r.IsIdle() {
 		err = cmn.NewErrAborted(r.Name(), "aborting non-idle", nil)
 
@@ -378,6 +378,9 @@ func (r *XactMoss) Abort(err error) bool {
 
 	hk.UnregIf(r.hkName(), func(int64) time.Duration { return 0 })
 
+	// unreg idle callback prior to quiesce
+	r.DemandBase.Stop()
+
 	nlog.Infoln(r.Name(), "aborting:", err)
 
 	r.activeWG.Wait()
@@ -389,8 +392,6 @@ func (r *XactMoss) Abort(err error) bool {
 
 	r.abortedWIDs.Clear()
 
-	r.DemandBase.Stop()
-
 	r.bewarmStop()
 	return true
 }
@@ -426,7 +427,9 @@ func (r *XactMoss) fini(int64) (d time.Duration) {
 	case r.Pending() > 0:
 		return mossIdleTime
 	default:
-		r.SetStopping()
+		if !r.SetStopping() {
+			return hk.UnregInterval
+		}
 
 		hk.UnregIf(r.hkName(), func(int64) time.Duration { return 0 })
 		// stop receiving
Original file line number	Diff line number	Diff line change
`@@ -43,7 +43,8 @@ type (`
`43`	`43`	`d atomic.Int64 // duration hk idle`
`44`	`44`	`last atomic.Int64 // mono.NanoTime`
`45`	`45`	`}`
`46`		`- pending atomic.Int64`
	`46`	`+ pending atomic.Int64`
	`47`	`+ unregged atomic.Bool // hk.Unreg() at most once per instance; NOTE: same-UUID renewals reuse HK names`
`47`	`48`	`}`
`48`	`49`	`)`
`49`	`50`
`@@ -76,7 +77,9 @@ func (r DemandBase) Init(uuid, kind string, bck meta.Bck, idleDur time.Duratio`
`76`	`77`	`r.InitBase(uuid, kind, bck)`
`77`	`78`
`78`	`79`	`r.idle.last.Store(mono.NanoTime())`
	`80`	`+`
`79`	`81`	`hk.Reg(r.hkName+hk.NameSuffix, r.hkcb, 0 /time.Duration/)`
	`82`	`+ r.unregged.Store(false)`
`80`	`83`	`}`
`81`	`84`
`82`	`85`	`// (e.g. usage: listed last page)`
`@@ -124,14 +127,19 @@ func (r *DemandBase) SubPending(n int) {`
`124`	`127`	`}`
`125`	`128`
`126`	`129`	`func (r *DemandBase) Stop() {`
	`130`	`+ if !r.unregged.CAS(false, true) {`
	`131`	`+ return`
	`132`	`+ }`
`127`	`133`	`r.SetStopping()`
`128`	`134`	`hk.Unreg(r.hkName + hk.NameSuffix)`
`129`	`135`	`if r.ticks != nil {`
`130`	`136`	`r.ticks.Close()`
`131`		`- r.ticks = nil`
`132`	`137`	`}`
`133`	`138`	`}`
`134`	`139`
	`140`	`+// Only abort the Base part, and note:`
	`141`	`+// for demand xactions, Stop() is a cleanup-sequence sensitive barrier: it unregisters`
	`142`	`+// the idle HK callback and can allow same-UUID renewal to register the same HK name.`
`135`	`143`	`func (r *DemandBase) Abort(err error) (ok bool) {`
`136`	`144`	`if err == nil && !r.IsIdle() {`
`137`	`145`	`err = cmn.NewErrAborted(r.Name(), "aborting non-idle", nil)`