lightning: fix panic when nextKey twice (#40959)

[ti-chi-bot]

This is an automated cherry-pick of #40959

Signed-off-by: lance6716 lance6716@gmail.com

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]

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• gozssky
• lance6716

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[sleepymole]

/merge

[ti-chi-bot]

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

Commit hash: 5c74ded

[sleepymole]

/retest

[sleepymole]

/retest

[sleepymole]

/retest