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etcdserver: fix panic when checking IsLearner of removed member #18606

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merged 1 commit into from
Oct 4, 2024
Merged

etcdserver: fix panic when checking IsLearner of removed member #18606

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4 changes: 3 additions & 1 deletion server/etcdserver/api/membership/cluster.go
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Original file line number Diff line number Diff line change
Expand Up @@ -817,8 +817,10 @@ func (c *RaftCluster) SetDowngradeInfo(d *serverversion.DowngradeInfo, shouldApp
// IsMemberExist returns if the member with the given id exists in cluster.
func (c *RaftCluster) IsMemberExist(id types.ID) bool {
c.Lock()
defer c.Unlock()
_, ok := c.members[id]
c.Unlock()

// gofail: var afterIsMemberExist struct{}
return ok
}

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7 changes: 4 additions & 3 deletions server/etcdserver/server.go
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Expand Up @@ -1224,7 +1224,8 @@ func (s *EtcdServer) isLeader() bool {

// MoveLeader transfers the leader to the given transferee.
func (s *EtcdServer) MoveLeader(ctx context.Context, lead, transferee uint64) error {
if !s.cluster.IsMemberExist(types.ID(transferee)) || s.cluster.Member(types.ID(transferee)).IsLearner {
member := s.cluster.Member(types.ID(transferee))
if member == nil || member.IsLearner {
return errors.ErrBadLeaderTransferee
}

Expand Down Expand Up @@ -1593,9 +1594,9 @@ func (s *EtcdServer) mayRemoveMember(id types.ID) error {
}

lg := s.Logger()
isLearner := s.cluster.IsMemberExist(id) && s.cluster.Member(id).IsLearner
member := s.cluster.Member(id)
// no need to check quorum when removing non-voting member
if isLearner {
if member != nil && member.IsLearner {
return nil
}

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48 changes: 48 additions & 0 deletions tests/integration/cluster_test.go
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Expand Up @@ -518,3 +518,51 @@ func TestSpeedyTerminate(t *testing.T) {
case <-donec:
}
}

// TestConcurrentRemoveMember demonstrated a panic in mayRemoveMember with
// concurrent calls to MemberRemove. To reliably reproduce the panic, a delay
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There should never be a concurrent call to MemberRemove. Cluster state changes should be all done via apply loop, which guarantees that there is only one concurrent change to cluster state.

The reason for locking in cluster struct (and any other internal structs) is to prevent reader+writer races. There should never be writer+writer race.

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This PR has nothing to do with the apply loop/workflow. It's fixing a panic in the API layer. Refer to #18606 (comment)

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Oh, I didn't notice that this is integration test. I'm just little confused why MemberRemove call by client is executed concurrently. Should it be linearized?

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I'm just little confused why MemberRemove call by client is executed concurrently.

Right, usually we don't expect users to do this. But etcdserver shouldn't panic due to whatever users' inappropriate behaviour. Note that the panicking happens at API layer instead of the apply loop/workflow.

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@serathius serathius Oct 4, 2024 •
edited
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Sorry, didn't mean "why?", but "how?". Agree that this is a problem, but I'm trying to understand how concurrency bug in cluster struct surfaces to API.

// needed to be injected in IsMemberExist, which is done using a failpoint.
// After fixing the bug, IsMemberExist is no longer called by mayRemoveMember.
func TestConcurrentRemoveMember(t *testing.T) {
integration.BeforeTest(t, integration.WithFailpoint("afterIsMemberExist", `sleep("1s")`))
c := integration.NewCluster(t, &integration.ClusterConfig{Size: 1})
defer c.Terminate(t)

addResp, err := c.Members[0].Client.MemberAddAsLearner(context.Background(), []string{"http://localhost:123"})
if err != nil {
t.Fatal(err)
}
removeID := addResp.Member.ID
done := make(chan struct{})
go func() {
time.Sleep(time.Second / 2)
c.Members[0].Client.MemberRemove(context.Background(), removeID)
close(done)
}()
if _, err := c.Members[0].Client.MemberRemove(context.Background(), removeID); err != nil {
t.Fatal(err)
}
<-done
}

func TestConcurrentMoveLeader(t *testing.T) {
integration.BeforeTest(t, integration.WithFailpoint("afterIsMemberExist", `sleep("1s")`))
c := integration.NewCluster(t, &integration.ClusterConfig{Size: 1})
defer c.Terminate(t)

addResp, err := c.Members[0].Client.MemberAddAsLearner(context.Background(), []string{"http://localhost:123"})
if err != nil {
t.Fatal(err)
}
removeID := addResp.Member.ID
done := make(chan struct{})
go func() {
time.Sleep(time.Second / 2)
c.Members[0].Client.MoveLeader(context.Background(), removeID)
close(done)
}()
if _, err := c.Members[0].Client.MemberRemove(context.Background(), removeID); err != nil {
t.Fatal(err)
}
<-done
}
4 changes: 2 additions & 2 deletions tests/robustness/makefile.mk
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Expand Up @@ -54,15 +54,15 @@ install-gofail: $(GOPATH)/bin/gofail

.PHONY: gofail-enable
gofail-enable: $(GOPATH)/bin/gofail
$(GOPATH)/bin/gofail enable server/etcdserver/ server/lease/leasehttp server/storage/backend/ server/storage/mvcc/ server/storage/wal/ server/etcdserver/api/v3rpc/
$(GOPATH)/bin/gofail enable server/etcdserver/ server/lease/leasehttp server/storage/backend/ server/storage/mvcc/ server/storage/wal/ server/etcdserver/api/v3rpc/ server/etcdserver/api/membership/
cd ./server && go get go.etcd.io/gofail@${GOFAIL_VERSION}
cd ./etcdutl && go get go.etcd.io/gofail@${GOFAIL_VERSION}
cd ./etcdctl && go get go.etcd.io/gofail@${GOFAIL_VERSION}
cd ./tests && go get go.etcd.io/gofail@${GOFAIL_VERSION}

.PHONY: gofail-disable
gofail-disable: $(GOPATH)/bin/gofail
$(GOPATH)/bin/gofail disable server/etcdserver/ server/lease/leasehttp server/storage/backend/ server/storage/mvcc/ server/storage/wal/ server/etcdserver/api/v3rpc/
$(GOPATH)/bin/gofail disable server/etcdserver/ server/lease/leasehttp server/storage/backend/ server/storage/mvcc/ server/storage/wal/ server/etcdserver/api/v3rpc/ server/etcdserver/api/membership/
cd ./server && go mod tidy
cd ./etcdutl && go mod tidy
cd ./etcdctl && go mod tidy
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