Unit test case 'executor TestIndexMergeRuntimeStats' fail on real TiKV

[tiancaiamao]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

I'm testing paging protocol by running tidb UT with a real TiKV using this branch #35647

tiup playground nightly --mode tikv-slim
cd executor
go test -run TestIndexMergeRuntimeStats -with-tikv 127.0.0.1:2379

2. What did you expect to see? (Required)

No error

3. What did you see instead (Required)

--- FAIL: TestIndexMergeRuntimeStats (3.79s)
    testkit.go:174: 
        	Error Trace:	testkit.go:174
        	            				testkit.go:168
        	            				testkit.go:108
        	            				executor_test.go:3070
        	Error:      	Received unexpected error:
        	            	runtime error: invalid memory address or nil pointer dereference
        	            	github.com/pingcap/tidb/store/copr.(*copIteratorWorker).handleTask.func1
        	            		/home/genius/project/src/github.com/pingcap/tidb/store/copr/coprocessor.go:664
        	            	runtime.gopanic
        	            		/home/genius/project/go/src/runtime/panic.go:838
        	            	runtime.panicmem
        	            		/home/genius/project/go/src/runtime/panic.go:220
        	            	runtime.sigpanic
        	            		/home/genius/project/go/src/runtime/signal_unix.go:818
        	            	github.com/pingcap/tidb/store/copr.(*copIteratorWorker).handleCopResponse
        	            		/home/genius/project/src/github.com/pingcap/tidb/store/copr/coprocessor.go:961
        	            	github.com/pingcap/tidb/store/copr.(*copIteratorWorker).handleTaskOnce
        	            		/home/genius/project/src/github.com/pingcap/tidb/store/copr/coprocessor.go:786
        	            	github.com/pingcap/tidb/store/copr.(*copIteratorWorker).handleTask
        	            		/home/genius/project/src/github.com/pingcap/tidb/store/copr/coprocessor.go:674
        	            	github.com/pingcap/tidb/store/copr.(*copIteratorWorker).run
        	            		/home/genius/project/src/github.com/pingcap/tidb/store/copr/coprocessor.go:416
        	            	runtime.goexit
        	            		/home/genius/project/go/src/runtime/asm_amd64.s:1571
        	Test:       	TestIndexMergeRuntimeStats
        	Messages:   	sql:select /*+ use_index_merge(t1, primary, t1a) */ * from t1 where id < 2 or a > 4 order by a, args:[]
FAIL

I've verified it's not caused by the changes from paging... instead, it's a bug on execution_info with cop cache.

4. What is your TiDB version? (Required)

master

commit 47a4f3a017768dda0b9a826451486c5539bc8427 (HEAD -> master, origin/master, origin/HEAD)
Author: Weizhen Wang <[email protected]>
Date:   Wed Jun 29 20:16:40 2022 +0800

    *: enable unconvert (#35821)
    
    ref pingcap/tidb#35345