stmtctx: add mutex to protect stmtCache(#36159) (#36351)

[ti-srebot]

cherry-pick #36351 to release-6.0
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/36390

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

git push [email protected]:ti-srebot/tidb.git pr/36390:release-6.0-5f3252c85bc9

---

What problem does this PR solve?

Issue Number: close #36159

Problem Summary: tidb_server panic which concurrently accessing stmtCache

What is changed and how it works?

stmtctx/stmtctx.go was changed, add mutex to protect stmtCache

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• jackysp

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[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.

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[ti-srebot]

/run-all-tests

[ti-srebot]

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

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/9482f502690c584ddff4f4140a5e878b7621045e

[jackysp]

LGTM

[jackysp]

PTAL @qw4990 @Reminiscent

[xhebox]

closed for DMR version