BenchmarkInsertChain_uncles panics

[meowsbits]

System information

> git rev-parse HEAD && go version && uname -a
111a1b73cfe87782ed34659f704bbea70b032e1e
go version go1.17.8 linux/amd64
Linux ubp52 5.2.9-050209-generic #201908160940 SMP Fri Aug 16 09:42:58 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

(111a1b7, current master head at time of writing)

Expected behaviour

Tests run and pass.

Actual behaviour

Tests panic at BenchmarkInsertChain_uncles_diskdb and BenchmarkInsertChain_uncles_memdb.
The parent variable value is nil in AddUncles in chain_makers.go.

Steps to reproduce the behaviour

go test -bench uncles ./core

Backtrace

[...]
BenchmarkInsertChain_uncles_memdb-12            t=2022-04-06T09:05:37-0700 lvl=info msg="Persisted trie from memory database"    nodes=1 size="165.00 B" time="4.53µs"   gcnodes=0 gcsize="0.00 B"   gctime=0s        livenodes=1  livesize="0.00 B"
t=2022-04-06T09:05:37-0700 lvl=dbug msg="Persisted trie from memory database"    nodes=3 size="425.00 B" time="5.939µs"  gcnodes=0 gcsize="0.00 B"   gctime=0s        livenodes=1  livesize="0.00 B"
t=2022-04-06T09:05:37-0700 lvl=dbug msg="Persisted trie from memory database"    nodes=2 size="261.00 B" time="3.17µs"
  gcnodes=0 gcsize="0.00 B"   gctime=0s        livenodes=1  livesize="0.00 B"
t=2022-04-06T09:05:37-0700 lvl=dbug msg="Persisted trie from memory database"    nodes=2 size="261.00 B" time="2.979µs"  gcnodes=0 gcsize="0.00 B"   gctime=0s        livenodes=1  livesize="0.00 B"
t=2022-04-06T09:05:37-0700 lvl=dbug msg="Persisted trie from memory database"    nodes=2 size="261.00 B" time="3.222µs"  gcnodes=0 gcsize="0.00 B"   gctime=0s        livenodes=1  livesize="0.00 B"
t=2022-04-06T09:05:37-0700 lvl=dbug msg="Persisted trie from memory database"    nodes=2 size="261.00 B" time="2.846µs"  gcnodes=0 gcsize="0.00 B"   gctime=0s        livenodes=1  livesize="0.00 B"
t=2022-04-06T09:05:37-0700 lvl=dbug msg="Persisted trie from memory database"    nodes=2 size="261.00 B" time="4.833µs"  gcnodes=0 gcsize="0.00 B"   gctime=0s        livenodes=1  livesize="0.00 B"
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x1c0 pc=0x7fcda2]

goroutine 98547 [running]:
github.com/ethereum/go-ethereum/consensus/ethash.CalcDifficulty(0x1039d40, 0x40fd07, 0x0)
        /home/ia/go/src/github.com/ethereum/go-ethereum/consensus/ethash/consensus.go:335 +0x42
github.com/ethereum/go-ethereum/consensus/ethash.(*Ethash).CalcDifficulty(0x77a36453b9905655, {0xae0288, 0xc008e50338}, 0x708be1f3980c4227, 0xc0373bd0e0)
        /home/ia/go/src/github.com/ethereum/go-ethereum/consensus/ethash/consensus.go:328 +0x45
github.com/ethereum/go-ethereum/core.(*BlockGen).AddUncle(0xc0441866e0, 0xc008ced200)
        /home/ia/go/src/github.com/ethereum/go-ethereum/core/chain_makers.go:169 +0x14e
github.com/ethereum/go-ethereum/core.genUncles(0xae3b80, 0xc008e500d0)
        /home/ia/go/src/github.com/ethereum/go-ethereum/core/bench_test.go:168 +0xaf
github.com/ethereum/go-ethereum/core.GenerateChain.func1(0x6, 0xc025d7bb00, 0xc0101e6d00)
        /home/ia/go/src/github.com/ethereum/go-ethereum/core/chain_makers.go:256 +0x486
github.com/ethereum/go-ethereum/core.GenerateChain(0xc0039fe300, 0xc025d7b680, {0xae8318, 0xc0102ce0e0}, {0xaee4c8, 0xc005fc2000}, 0x64, 0xa32870)
        /home/ia/go/src/github.com/ethereum/go-ethereum/core/chain_makers.go:279 +0x22d
github.com/ethereum/go-ethereum/core.benchInsertChain(0xc008c6c000, 0x79, 0x1071920)
        /home/ia/go/src/github.com/ethereum/go-ethereum/core/bench_test.go:200 +0x4fa
github.com/ethereum/go-ethereum/core.BenchmarkInsertChain_uncles_memdb(0xc008c6c000)
        /home/ia/go/src/github.com/ethereum/go-ethereum/core/bench_test.go:56 +0x25
testing.(*B).runN(0xc008c6c000, 0x64)
        /home/ia/go1.17.8.linux-amd64/src/testing/benchmark.go:192 +0x126
testing.(*B).launch(0xc008c6c000)
        /home/ia/go1.17.8.linux-amd64/src/testing/benchmark.go:328 +0x1c5
created by testing.(*B).doBench
        /home/ia/go1.17.8.linux-amd64/src/testing/benchmark.go:283 +0x7b
exit status 2
FAIL    github.com/ethereum/go-ethereum/core    54.426s
FAIL

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[rjl493456442]

Thanks for catching it, the fix is opened.