schedule: fix panic when switching placement rules (#7415)

[ti-chi-bot]

This is an automated cherry-pick of #7415

What problem does this PR solve?

Issue Number: Close #7414.

What is changed and how does it work?

When we going to disable the placement rule, we might first check:

pd/pkg/schedule/checker/checker_controller.go

Line 89 in 8e6dcfb

if c.conf.IsPlacementRulesEnabled() {

Before we change it, the value is true. But when we call:

pd/pkg/schedule/checker/checker_controller.go

Line 102 in 8e6dcfb

fit := c.priorityInspector.Inspect(region)

pd/pkg/schedule/checker/priority_inspector.go

Lines 64 to 74 in 8e6dcfb

	func (p *PriorityInspector) Inspect(region *core.RegionInfo) (fit *placement.RegionFit) {
	var makeupCount int
	if p.conf.IsPlacementRulesEnabled() {
	makeupCount, fit = p.inspectRegionInPlacementRule(region)
	} else {
	makeupCount = p.inspectRegionInReplica(region)
	}
	priority := 0 - makeupCount
	p.addOrRemoveRegion(priority, region.GetID())
	return
	}

The value can be changed to false. So the fit will be nil in this case.

Check List

Tests

• Unit test

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• lhy1024

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[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
Adding the do-not-merge/cherry-pick-not-approved label.

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[lhy1024]

need fix conflict

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 75.52%. Comparing base (b092996) to head (9f10745).
Report is 6 commits behind head on release-6.1.

Files with missing lines	Patch %	Lines
server/schedule/checker/rule_checker.go	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           release-6.1    #7422      +/-   ##
===============================================
+ Coverage        75.39%   75.52%   +0.12%     
===============================================
  Files              308      308              
  Lines            30591    30593       +2     
===============================================
+ Hits             23063    23104      +41     
+ Misses            5516     5484      -32     
+ Partials          2012     2005       -7     

Flag	Coverage Δ
unittests	75.52% <0.00%> (+0.12%)	⬆️

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lhy1024, rleungx

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• OWNERS [lhy1024,rleungx]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-09-10 07:21:31.748737497 +0000 UTC m=+340961.489161421: ☑️ agreed by rleungx.
• 2024-09-10 07:22:28.28341019 +0000 UTC m=+341018.023834129: ☑️ agreed by lhy1024.

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