Concurrent access can cause deadlock

[willscott]

Observed hang during fuzz testing

program hanged (timeout 10 seconds)

SIGABRT: abort
PC=0x462f01 m=0 sigcode=0

goroutine 0 [idle]:
runtime.futex(0x79b768, 0x80, 0x0, 0x0, 0x7ffd00000000, 0x462b25, 0xbb93a, 0x21d6076d, 0x7ffd8175da28, 0x40b37f, ...)
	runtime/sys_linux_amd64.s:567 +0x21
runtime.futexsleep(0x79b768, 0x0, 0xffffffffffffffff)
	runtime/os_linux.go:45 +0x46
runtime.notesleep(0x79b768)
	runtime/lock_futex.go:151 +0x9f
runtime.stopm()
	runtime/proc.go:1828 +0xc0
runtime.findrunnable(0xc000022000, 0x0)
	runtime/proc.go:2360 +0xa0d
runtime.schedule()
	runtime/proc.go:2520 +0x2fc
runtime.park_m(0xc000001200)
	runtime/proc.go:2690 +0x9d
runtime.mcall(0x0)
	runtime/asm_amd64.s:318 +0x5b

goroutine 1 [chan send]:
github.com/ipfs/go-datastore/fuzz.(*RunState).Fuzz(0xc00005e000, 0x7f1b500e8000, 0xe1, 0xe1)
	/home/user/Documents/github/go-datastore/fuzz/fuzzer.go:162 +0x68
github.com/ipfs/go-datastore/fuzz.FuzzDB(0x61df53, 0xd, 0xc00001c120, 0x13, 0xc00001c101, 0x7f1b500e8000, 0xe1, 0xe1, 0x2cd8fea415bd5245)
	/home/user/Documents/github/go-datastore/fuzz/fuzzer.go:142 +0x10e
github.com/ipfs/go-datastore/fuzz.Fuzz(0x7f1b500e8000, 0xe1, 0xe1, 0x4)
	/home/user/Documents/github/go-datastore/fuzz/fuzzer.go:128 +0x334
go-fuzz-dep.Main(0xc000044f70, 0x1, 0x1)
	go-fuzz-dep/main.go:36 +0x1ad
main.main()
	github.com/ipfs/go-datastore/fuzz/go.fuzz.main/main.go:15 +0x52

goroutine 3 [select]:
github.com/syndtr/goleveldb/leveldb/util.(*BufferPool).drain(0xc00006a000)
	/home/user/Documents/local/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/util/buffer_pool.go:206 +0x1b1
created by github.com/syndtr/goleveldb/leveldb/util.NewBufferPool
	/home/user/Documents/local/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/util/buffer_pool.go:237 +0x212

goroutine 5 [select]:
github.com/syndtr/goleveldb/leveldb.(*DB).compactionError(0xc0000bc820)
	/home/user/Documents/local/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/db_compaction.go:90 +0x117
created by github.com/syndtr/goleveldb/leveldb.openDB
	/home/user/Documents/local/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/db.go:142 +0x4f2

goroutine 6 [select]:
github.com/syndtr/goleveldb/leveldb.(*DB).mpoolDrain(0xc0000bc820)
	/home/user/Documents/local/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/db_state.go:101 +0x108
created by github.com/syndtr/goleveldb/leveldb.openDB
	/home/user/Documents/local/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/db.go:143 +0x514

goroutine 7 [select]:
github.com/syndtr/goleveldb/leveldb.(*DB).tCompaction(0xc0000bc820)
	/home/user/Documents/local/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/db_compaction.go:825 +0x2ba
created by github.com/syndtr/goleveldb/leveldb.openDB
	/home/user/Documents/local/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/db.go:149 +0x6b0

goroutine 8 [select]:
github.com/syndtr/goleveldb/leveldb.(*DB).mCompaction(0xc0000bc820)
	/home/user/Documents/local/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/db_compaction.go:762 +0x1a0
created by github.com/syndtr/goleveldb/leveldb.openDB
	/home/user/Documents/local/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/db.go:150 +0x6d2

goroutine 9 [semacquire]:
sync.runtime_Semacquire(0xc00005e030)
	runtime/sema.go:56 +0x42
sync.(*WaitGroup).Wait(0xc00005e028)
	sync/waitgroup.go:130 +0x64
github.com/ipfs/go-datastore/fuzz.Open.func2(0xc00005e000, 0xc00000e001, 0xc00001c120, 0x13, 0xc0000965a0)
	/home/user/Documents/github/go-datastore/fuzz/fuzzer.go:96 +0x4b
created by github.com/ipfs/go-datastore/fuzz.Open
	/home/user/Documents/github/go-datastore/fuzz/fuzzer.go:95 +0x2dd

goroutine 10 [select]:
github.com/syndtr/goleveldb/leveldb.(*DB).putRec(0xc0000bc820, 0x0, 0xc000016620, 0x1, 0x8, 0x0, 0x0, 0x0, 0xc000016628, 0x1, ...)
	/home/user/Documents/local/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/db_write.go:330 +0x3f7
github.com/syndtr/goleveldb/leveldb.(*DB).Delete(0xc0000bc820, 0xc000016620, 0x1, 0x8, 0xc000016628, 0x8, 0x2d)
	/home/user/Documents/local/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/db_write.go:381 +0x8f
github.com/ipfs/go-ds-leveldb.(*accessor).Delete(0xc00000e0a0, 0x61c362, 0x1, 0x0, 0x0)
	/home/user/Documents/local/go/pkg/mod/github.com/ipfs/go-ds-leveldb@v0.4.2/datastore.go:118 +0x13a
github.com/ipfs/go-datastore/fuzz.nextState(0xc00003ef30, 0xc00003ee82, 0x0, 0x0)
	/home/user/Documents/github/go-datastore/fuzz/fuzzer.go:265 +0x66f
github.com/ipfs/go-datastore/fuzz.threadDriver(0x6591e0, 0xc000090040, 0xc00005e000, 0xc0000fe000)
	/home/user/Documents/github/go-datastore/fuzz/fuzzer.go:208 +0x173
created by github.com/ipfs/go-datastore/fuzz.Open
	/home/user/Documents/github/go-datastore/fuzz/fuzzer.go:107 +0x3dd