Fix level db panic

[michaelavila]

This PR exists for me to trouble shoot some CI issues. Disregard.

[Stebalien]

#6185?

[michaelavila]

@Stebalien I'm actually using this PR to troubleshoot the leveldb panics as I can't reproduce them locally. Are you saying #6185 should fix that?

[Stebalien]

Ah, no. Sorry, different issue.

In terms of the leveldb panics, I think we're closing the datastore while reading from it (or reading from it after closing it?).

[michaelavila]

@Stebalien yeah, there are those panics and there's also the panic from the pinning test:

panic: interface conversion: cache.Value is nil, not *table.Reader

goroutine 103 [running]:
github.com/syndtr/goleveldb/leveldb.(*tOps).find(0xc00034fc20, 0xc0001bc0f0, 0xc000456090, 0x2b, 0x2b, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
	/home/circleci/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/table.go:383 +0x221
github.com/syndtr/goleveldb/leveldb.(*version).get.func1(0x0, 0xc0001bc0f0, 0xc000456090)
	/home/circleci/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/version.go:176 +0x452
github.com/syndtr/goleveldb/leveldb.(*version).walkOverlapping(0xc000330a50, 0x0, 0x0, 0x0, 0xc000456090, 0x2b, 0x2b, 0xc000347910, 0xc0003478e0)
	/home/circleci/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/version.go:116 +0x2a7
github.com/syndtr/goleveldb/leveldb.(*version).get(0xc000330a50, 0x0, 0x0, 0x0, 0xc000456090, 0x2b, 0x2b, 0x0, 0x0, 0x0, ...)
	/home/circleci/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/version.go:160 +0x2b2
github.com/syndtr/goleveldb/leveldb.(*DB).get(0xc000286000, 0x0, 0x0, 0x0, 0x0, 0xc000456060, 0x23, 0x30, 0x1d, 0x0, ...)
	/home/circleci/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/db.go:779 +0x397
github.com/syndtr/goleveldb/leveldb.(*DB).Get(0xc000286000, 0xc000456060, 0x23, 0x30, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0)
	/home/circleci/go/pkg/mod/github.com/syndtr/goleveldb@v1.0.0/leveldb/db.go:845 +0x12f
github.com/ipfs/go-ds-leveldb.(*accessor).Get(0xc000190a20, 0xc000456030, 0x23, 0x0, 0x0, 0x0, 0x0, 0x0)
	/home/circleci/go/pkg/mod/github.com/ipfs/go-ds-leveldb@v0.0.1/datastore.go:84 +0x82
github.com/ipfs/go-ds-measure.(*measure).Get(0xc0001de000, 0xc000456030, 0x23, 0x0, 0x0, 0x0, 0x0, 0x0)
	/home/circleci/go/pkg/mod/github.com/ipfs/go-ds-measure@v0.0.1/measure.go:149 +0xd4
github.com/ipfs/go-datastore/mount.(*Datastore).Get(0xc0001942c0, 0xc000456000, 0x23, 0x24bcc00, 0xbf21969c66d5cebf, 0x1336e5a, 0x249da20, 0x23)
	/home/circleci/go/pkg/mod/github.com/ipfs/go-datastore@v0.0.2/mount/mount.go:197 +0x70
github.com/ipfs/go-ds-measure.(*measure).Get(0xc0001de240, 0xc000456000, 0x23, 0x0, 0x0, 0x0, 0x0, 0x0)
	/home/circleci/go/pkg/mod/github.com/ipfs/go-ds-measure@v0.0.1/measure.go:149 +0xd4
github.com/ipfs/go-datastore/keytransform.(*ktds).Get(0xc000336400, 0xc0001ac040, 0x11, 0x1, 0xc0001ae090, 0x10, 0x14a5580, 0x24bdfe0)
	/home/circleci/go/pkg/mod/github.com/ipfs/go-datastore@v0.0.2/keytransform/keytransform.go:40 +0x76
github.com/ipfs/go-ipfs/provider.(*Queue).nextEntry(0xc0004d8a50, 0x0, 0x0, 0xc00009d601, 0xc00009d698)
	/home/circleci/ipfs/go-ipfs/provider/queue.go:73 +0xc2
github.com/ipfs/go-ipfs/provider.(*Queue).work.func1(0xc0004d8a50)
	/home/circleci/ipfs/go-ipfs/provider/queue.go:107 +0x6d1
created by github.com/ipfs/go-ipfs/provider.(*Queue).work
	/home/circleci/ipfs/go-ipfs/provider/queue.go:101 +0x4f

They could be related. The other panics (the 10:56:51.864 ERROR provider: Failed to enqueue cid: leveldb: closed queue.go:121) are just being logged and swallowed up, but the panic in the middle of the pinning test is different and actually panicking ipfs, so I'm a little more worried about it.

[michaelavila]

@Stebalien we had something like your suggestion earlier, but ran into some issues that I didn't this time around. Changes are in. Let me know if you had something else in mind.

[Stebalien]

Ok, one more blocker down. Thanks!