loki_querier_tail_active and loki_querier_tail_active_streams metrics become negative

[umezawatakeshi]

Describe the bug loki_querier_tail_active and loki_querier_tail_active_streams are positive or zero soon after boot but become negative some time after.

To Reproduce Steps to reproduce the behavior:

1. Started Loki v3.2.1
2. Started many loki-canary
3. Query: loki_querier_tail_active or loki_querier_tail_active_streams

Expected behavior These metrics shows the number of tail connections and streams, which are always positive or zero.

Environment:

• Infrastructure: k8s 1.29
• Deployment tool: jsonnet

Screenshots, Promtail config, or terminal output

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These metrics are incremented at https://github.com/grafana/loki/blob/v3.2.1/pkg/querier/tail.go#L344 and https://github.com/grafana/loki/blob/v3.2.1/pkg/querier/tail.go#L303 , and decremented at https://github.com/grafana/loki/blob/v3.2.1/pkg/querier/tail.go#L272-L273 and no other code modify them. Is Tailer.close() called multiple times?