region_cache: filter peers on tombstone or dropped stores (#24726)

[ti-srebot]

cherry-pick #24726 to release-4.0
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/25836

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/tidb.git pr/25836:release-4.0-55d26c583230

---

Signed-off-by: youjiali1995 zlwgx1023@gmail.com

What problem does this PR solve?

Issue Number: close #24648

Problem Summary:

TiDB doesn't handle tombstone or dropped stores correctly. It may report an error if there is a peer on such a store.

What is changed and how it works?

What's Changed:

1. Add a tombstone state which means the store is a tombstone.
2. Filter peers on tombstone or dropped stores and add a backoffer to Region.init().
3. Fix data race between asyncCheckAndResolveLoop() and initResolve(). Now unresolved stores will only be resolved by initResolve().

How it Works:

Check List

Tests

• Unit test

Side effects

Release note

• No release note.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has not been approved.

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[ti-chi-bot]

@ti-srebot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick, it must first be approved by the collaborators.

AFTER it has been approved by collaborators, please ping the release team in a comment to request a cherry pick review.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[ti-srebot]

/run-all-tests

[ti-srebot]

@youjiali1995 you're already a collaborator in bot's repo.