schedule: fix panic when switching placement rules

[rleungx]

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]

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• bufferflies
• lhy1024

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[lhy1024]

Do we need to pick it to other branches?

[codecov]

Codecov Report

Merging #7415 (f0c97e9) into master (8198735) will increase coverage by 0.08%.
Report is 1 commits behind head on master.
The diff coverage is 0.00%.

❗ Current head f0c97e9 differs from pull request most recent head 09394e2. Consider uploading reports for the commit 09394e2 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7415      +/-   ##
==========================================
+ Coverage   74.21%   74.29%   +0.08%     
==========================================
  Files         451      451              
  Lines       49385    49388       +3     
==========================================
+ Hits        36652    36694      +42     
+ Misses       9461     9432      -29     
+ Partials     3272     3262      -10     

Flag	Coverage Δ
unittests	74.29% <0.00%> (+0.08%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

[bufferflies]

Do we need to add one metrics for it or add log?

[rleungx]

I think no need since it happens only once.

[rleungx]

/merge

[ti-chi-bot]

@rleungx: It seems you want to merge this PR, I will help you trigger all the tests:

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[ti-chi-bot]

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

Commit hash: f0c97e9

[ti-chi-bot]

@rleungx: Your PR was out of date, I have automatically updated it for you.

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.1: #7422.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #7423.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #7424.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #7425.