lightning: fix panic when nextKey twice (#40959)

[lance6716]

manually cherry-pick #40959

What problem does this PR solve?

Issue Number: close #40934

Problem Summary:

What is changed and how it works?

Avoid to let CommonHandle++ and decode it because the result may not be a valid value. The string datum encoding will not be ended with 0xff and we may increase 0xfe to 0xff.

tidb/util/codec/bytes.go

Lines 35 to 49 in 151cd7e

	// EncodeBytes guarantees the encoded value is in ascending order for comparison,
	// encoding with the following rule:
	//
	// [group1][marker1]...[groupN][markerN]
	// group is 8 bytes slice which is padding with 0.
	// marker is `0xFF - padding 0 count`
	//
	// For example:
	//
	// [] -> [0, 0, 0, 0, 0, 0, 0, 0, 247]
	// [1, 2, 3] -> [1, 2, 3, 0, 0, 0, 0, 0, 250]
	// [1, 2, 3, 0] -> [1, 2, 3, 0, 0, 0, 0, 0, 251]
	// [1, 2, 3, 4, 5, 6, 7, 8] -> [1, 2, 3, 4, 5, 6, 7, 8, 255, 0, 0, 0, 0, 0, 0, 0, 0, 247]
	//
	// Refer: https://github.com/facebook/mysql-5.6/wiki/MyRocks-record-format#memcomparable-format

Check List

Tests

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

Run the changed tests and failpoints will trigger this panic. And after the fix it is avoided.

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x68 pc=0x34e93e5]

goroutine 436 [running]:
github.com/pingcap/tidb/br/pkg/lightning/backend/local.nextKey({0xc000874f18, 0x0?, 0x119?})
        /home/lance/Projects/tidb/br/pkg/lightning/backend/local/local.go:2069 +0x85
github.com/pingcap/tidb/br/pkg/lightning/backend/local.(*local).SplitAndScatterRegionByRanges(0xc000fe6dc0, {0x4fc3aa8?, 0xc001150140?}, {0xc0011a4900, 0x1, 0x576921f?}, 0xc00069e330, 0x1, 0x6000000)
        /home/lance/Projects/tidb/br/pkg/lightning/backend/local/localhelper.go:328 +0x1dd9
github.com/pingcap/tidb/br/pkg/lightning/backend/local.(*local).SplitAndScatterRegionInBatches(0x489294d?, {0x4fc3aa8, 0xc001150140}, {0xc0011a4900, 0x1, 0x1}, 0xc000fde240?, 0x1b?, 0x0?, 0x1000)
        /home/lance/Projects/tidb/br/pkg/lightning/backend/local/localhelper.go:80 +0x125
github.com/pingcap/tidb/br/pkg/lightning/backend/local.(*local).ImportEngine(0xc000fe6dc0, {0x4fc3aa8, 0xc001150140}, {0xf, 0x31, 0x82, 0xea, 0x38, 0xf9, 0x59, ...}, ...)
        /home/lance/Projects/tidb/br/pkg/lightning/backend/local/local.go:1661 +0x13ed
github.com/pingcap/tidb/br/pkg/lightning/backend.(*ClosedEngine).Import(0xc0006da960, {0x4fc3aa8, 0xc001150140}, 0xc0005370a0?, 0x0?)
        /home/lance/Projects/tidb/br/pkg/lightning/backend/backend.go:477 +0x23b
github.com/pingcap/tidb/br/pkg/lightning/restore.(*TableRestore).importKV(0xc000deaf80, {0x4fc3aa8, 0xc001150140}, 0xc0006da960, 0xc0009ff6c0, 0x7523580?)
        /home/lance/Projects/tidb/br/pkg/lightning/restore/table_restore.go:1004 +0x207
github.com/pingcap/tidb/br/pkg/lightning/restore.(*TableRestore).importEngine(0xc001254540?, {0x4fc3aa8?, 0xc001150140}, 0x0?, 0xc0009ff6c0, 0x0?, 0x0?)
        /home/lance/Projects/tidb/br/pkg/lightning/restore/table_restore.go:703 +0x4c
github.com/pingcap/tidb/br/pkg/lightning/restore.(*TableRestore).restoreEngines.func3(0x0?, 0x0, 0xc0005a1400)
        /home/lance/Projects/tidb/br/pkg/lightning/restore/table_restore.go:331 +0x2ed
created by github.com/pingcap/tidb/br/pkg/lightning/restore.(*TableRestore).restoreEngines
        /home/lance/Projects/tidb/br/pkg/lightning/restore/table_restore.go:322 +0x1499
make: *** [Makefile:324: br_integration_test] Error 2

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:

• gozssky
• lichunzhu

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.

[lance6716]

/test build

[lance6716]

/merge

[ti-chi-bot]

@lance6716: /merge in this pull request requires 2 approval(s).

In response to this:

/merge

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 ti-community-infra/tichi repository.

[lichunzhu]

LGTM

[lichunzhu]

/merge

[lance6716]

/merge

[ti-chi-bot]

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

Commit hash: c941af3

[ti-chi-bot]

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

Commit hash: c941af3

[ti-chi-bot]

@lance6716: Your PR was out of date, I have automatically updated it for you.

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

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 ti-community-infra/tichi repository.

[lance6716]

/retest

[lance6716]

/retest

[hawkingrei]

/test unit-test