session: fix data race in ParseWithParamsInternal

[Defined2014]

What problem does this PR solve?

Issue Number: close #30918

Problem Summary:

What is changed and how it works?

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

fix data race in `ParseWithParamsInternal`

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• wjhuang2016
• xhebox

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[Defined2014]

/cc @wjhuang2016 @xhebox @tiancaiamao @hawkingrei
PTAL

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/0f61034c2c3ed4b31107914e98ef54b5c3057178

[tiancaiamao]

The design of this function is problematic, the parse and the execute is not using the same session.
If the SQL has some side-effect, for example, a warning message, it's left on the pool's session.

A better solution is a callback style API:

func (s *session) runWithInternalSQLExec(fn func(exec sqlexec.RestrictedSQLExec) error) {
    tmp, err := s.sysSessionPool().Get()
	if err != nil {
		return nil, err
	}
	defer s.sysSessionPool().Put(tmp)
    se := tmp.(*session)
    return fn(se)
}

The call use it like this:

se.runWithInternalSQLExec(func(exec *exec.RestrictedSQLExec) {
    stmt := exec.ParseWithParamsInternal(...)
    exec.Exec(stmt)
    ...
})

And you can finally wrap a simpler API like:

func (s *session) ExecRestrictedSQL(sql string) {
    s.runWithInternalSQLExec(func(exec sqlexec.RestrictedSQLExec) {
        stmt := exec.ParseWithParamsInternal(...)
        exec.Exec(stmt)
        ...        
    })
}

The simplied API is more convenient, but its design is not secure.

[Defined2014]

But we didn't use same session before. And I don't know it's a bug or a feature 😭.
The ExecRestrictedStmt will get a session from session pool, and it is not same as parser's.

[tiancaiamao]

But we didn't use same session before. And I don't know it's a bug or feature 😭.

Before a previous refactoring, they're in the same session.
The data race is introduced after that refactoring

[Defined2014]

Fix the data race fisrt, it may affects 5.4.0.

[tiancaiamao]

@hawkingrei are you also working on this? we should avoid repeated working

[hawkingrei]

@hawkingrei are you also working on this? we should avoid repeated working

No, I am not refactoring. I just fix the data race problem.

[hawkingrei]

@hawkingrei are you also working on this? we should avoid repeated working

No, I am not refactoring. I just fix the data race problem.

I can provide the necessary help.

[Defined2014]

/label needs-cherry-pick-5.4

[xhebox]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 07a1f47

[Defined2014]

/merge

[ti-chi-bot]

@Defined2014: /merge is only allowed for the committers, you can assign this pull request to the committer in list by filling /assign @committer in the comment to help merge this pull request.

In response to this:

/merge

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[xhebox]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 92cf9e5

[Defined2014]

/run-mysql-test

[Defined2014]

/run-unit-test

[Defined2014]

/run-check_dev_2

[Defined2014]

/run-mysql-test

[ti-srebot]

cherry pick to release-5.4 in PR #31404