invoke the Lock function in concurrency package will get stuck in when etcd servers are not available

[littlekuo]

Bug report criteria

• This bug report is not security related, security issues should be disclosed privately via etcd maintainers.
• This is not a support request or question, support requests or questions should be raised in the etcd discussion forums.
• You have read the etcd bug reporting guidelines.
• Existing open issues along with etcd frequently asked questions have been checked and this is not a duplicate.

What happened?

when etcd servers are not available, invoke the Lock function maybe stuck in the following places because client.cancel() only be invoked when client close, but usually we only close client when process exit.

m.Unlock(client.Ctx()) maybe should be changed to m.Unlock(ctx) which ctx is the param of Lock func?

What did you expect to happen?

nothing

How can we reproduce it (as minimally and precisely as possible)?

see the description

Anything else we need to know?

No response

Etcd version (please run commands below)

$ etcd --version
# paste output here

$ etcdctl version
# paste output here

Etcd configuration (command line flags or environment variables)

paste your configuration here

Etcd debug information (please run commands below, feel free to obfuscate the IP address or FQDN in the output)

$ etcdctl member list -w table
# paste output here

$ etcdctl --endpoints=<member list> endpoint status -w table
# paste output here

Relevant log output

No response