diff --git a/sched.go b/sched.go
index ed648bf19..e8eda4834 100644
--- a/sched.go
+++ b/sched.go
@@ -52,7 +52,7 @@ type WorkerSelector interface {
 type scheduler struct {
 	spt abi.RegisteredSealProof
 
-	workersLk  sync.Mutex
+	workersLk  sync.RWMutex
 	nextWorker WorkerID
 	workers    map[WorkerID]*workerHandle
 
@@ -83,6 +83,8 @@ type workerHandle struct {
 	preparing *activeResources
 	active    *activeResources
 
+	lk sync.Mutex
+
 	// stats / tracking
 	wt *workTracker
 
@@ -283,6 +285,9 @@ func (sh *scheduler) trySched() {
 
 	log.Debugf("SCHED %d queued; %d open windows", sh.schedQueue.Len(), len(windows))
 
+	sh.workersLk.RLock()
+	defer sh.workersLk.RUnlock()
+
 	// Step 1
 	for sqi := 0; sqi < sh.schedQueue.Len(); sqi++ {
 		task := (*sh.schedQueue)[sqi]
@@ -428,9 +433,9 @@ func (sh *scheduler) runWorker(wid WorkerID) {
 	defer ready.Wait()
 
 	go func() {
-		sh.workersLk.Lock()
+		sh.workersLk.RLock()
 		worker, found := sh.workers[wid]
-		sh.workersLk.Unlock()
+		sh.workersLk.RUnlock()
 
 		ready.Done()
 
@@ -498,16 +503,19 @@ func (sh *scheduler) runWorker(wid WorkerID) {
 					todo := activeWindows[0].todo[0]
 					needRes := ResourceTable[todo.taskType][sh.spt]
 
-					sh.workersLk.Lock()
+					sh.workersLk.RLock()
+					worker.lk.Lock()
 					ok := worker.preparing.canHandleRequest(needRes, wid, worker.info.Resources)
+					worker.lk.Unlock()
+
 					if !ok {
-						sh.workersLk.Unlock()
+						sh.workersLk.RUnlock()
 						break assignLoop
 					}
 
 					log.Debugf("assign worker sector %d", todo.sector.Number)
 					err := sh.assignWorker(taskDone, wid, worker, todo)
-					sh.workersLk.Unlock()
+					sh.workersLk.RUnlock()
 
 					if err != nil {
 						log.Error("assignWorker error: %+v", err)
@@ -530,14 +538,18 @@ func (sh *scheduler) runWorker(wid WorkerID) {
 func (sh *scheduler) assignWorker(taskDone chan struct{}, wid WorkerID, w *workerHandle, req *workerRequest) error {
 	needRes := ResourceTable[req.taskType][sh.spt]
 
+	w.lk.Lock()
 	w.preparing.add(w.info.Resources, needRes)
+	w.lk.Unlock()
 
 	go func() {
 		err := req.prepare(req.ctx, w.wt.worker(w.w))
 		sh.workersLk.Lock()
 
 		if err != nil {
+			w.lk.Lock()
 			w.preparing.free(w.info.Resources, needRes)
+			w.lk.Unlock()
 			sh.workersLk.Unlock()
 
 			select {
@@ -557,7 +569,9 @@ func (sh *scheduler) assignWorker(taskDone chan struct{}, wid WorkerID, w *worke
 		}
 
 		err = w.active.withResources(wid, w.info.Resources, needRes, &sh.workersLk, func() error {
+			w.lk.Lock()
 			w.preparing.free(w.info.Resources, needRes)
+			w.lk.Unlock()
 			sh.workersLk.Unlock()
 			defer sh.workersLk.Lock() // we MUST return locked from this function