Segmentation fault in 1.9.0-unstable

[Bobface]

Command:
geth --syncmode=fast --cache 8192 --ipcpath=/root/gethipc/

Version:

Geth
Version: 1.9.0-unstable
Git Commit: 313576530fe2ca0d37c6ddcdd8441030176c6c61
Architecture: amd64
Protocol Versions: [63 62]
Network Id: 1
Go Version: go1.10.4
Operating System: linux
GOPATH=
GOROOT=/usr/lib/go-1.10

Panic:

INFO [03-01|23:59:32.183] Imported new state entries               count=1536 elapsed=11.154ms  processed=23778463 pending=4757  retry=0   duplicate=2275 unexpected=18109
INFO [03-01|23:59:33.218] Imported new state entries               count=1920 elapsed=13.518ms  processed=23780383 pending=3748  retry=0   duplicate=2275 unexpected=18109
INFO [03-01|23:59:33.334] Imported new block headers               count=1    elapsed=4.961ms   number=7286576 hash=fc6817…438906
INFO [03-01|23:59:33.680] Imported new state entries               count=1920 elapsed=15.010ms  processed=23782303 pending=2392  retry=0   duplicate=2275 unexpected=18109
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x6c796a]

goroutine 375 [running]:
github.com/ethereum/go-ethereum/core/types.(*Block).Hash(0x0, 0x0, 0x0, 0x0, 0x0)
        /mnt/Geth/go-ethereum/build/_workspace/src/github.com/ethereum/go-ethereum/core/types/block.go:362 +0x4a
github.com/ethereum/go-ethereum/core.(*BlockChain).Rollback(0xc47794c000, 0xc4ba4f0000, 0x800, 0x800)
        /mnt/Geth/go-ethereum/build/_workspace/src/github.com/ethereum/go-ethereum/core/blockchain.go:780 +0x43d
github.com/ethereum/go-ethereum/eth/downloader.(*Downloader).processHeaders.func1(0xc42008dd30, 0xc420273d40)
        /mnt/Geth/go-ethereum/build/_workspace/src/github.com/ethereum/go-ethereum/eth/downloader/downloader.go:1305 +0x20d
github.com/ethereum/go-ethereum/eth/downloader.(*Downloader).processHeaders(0xc420273d40, 0x6f2f31, 0x6f2514, 0xc479c18e00, 0x117dfe0, 0xc42020f6d0)
        /mnt/Geth/go-ethereum/build/_workspace/src/github.com/ethereum/go-ethereum/eth/downloader/downloader.go:1324 +0x123d
github.com/ethereum/go-ethereum/eth/downloader.(*Downloader).syncWithPeer.func6(0x8, 0x10854b0)
        /mnt/Geth/go-ethereum/build/_workspace/src/github.com/ethereum/go-ethereum/eth/downloader/downloader.go:475 +0x49
github.com/ethereum/go-ethereum/eth/downloader.(*Downloader).spawnSync.func1(0xc420273d40, 0xc479e34d20, 0xc479a9bce0)
        /mnt/Geth/go-ethereum/build/_workspace/src/github.com/ethereum/go-ethereum/eth/downloader/downloader.go:492 +0x59
created by github.com/ethereum/go-ethereum/eth/downloader.(*Downloader).spawnSync
        /mnt/Geth/go-ethereum/build/_workspace/src/github.com/ethereum/go-ethereum/eth/downloader/downloader.go:492 +0xaf

[holiman]

https://github.com/ethereum/go-ethereum/blob/master/core/blockchain.go#L780

		if currentFastBlock := bc.CurrentFastBlock(); currentFastBlock.Hash() == hash {
			newFastBlock := bc.GetBlock(currentFastBlock.ParentHash(), currentFastBlock.NumberU64()-1)
			bc.currentFastBlock.Store(newFastBlock)
			rawdb.WriteHeadFastBlockHash(bc.db, newFastBlock.Hash())
}

For some reason, newFastBlock appears to be nil

[holiman]

We think the root cause for issues like this should have been fixed by #20287 . Closing this, please reopen (or open a new ticket) if you hit it again.