internal/batchskl: checkptr: unsafe pointer conversion #667
Description
Go 1.14 adds a new checkptr compile flag which is enabled when running with -race. Running go test -race ./internal/batchskl w/ Go 1.14 produces:
fatal error: checkptr: unsafe pointer conversion
goroutine 36 [running]:
runtime.throw(0x184eb61, 0x23)
/usr/local/Cellar/go/1.14/libexec/src/runtime/panic.go:1112 +0x72 fp=0xc00006caa0 sp=0xc00006ca70 pc=0x1073af2
runtime.checkptrAlignment(0xc000180b70, 0x1801a40, 0x1)
/usr/local/Cellar/go/1.14/libexec/src/runtime/checkptr.go:18 +0xb7 fp=0xc00006cad0 sp=0xc00006caa0 pc=0x1045a97
github.com/cockroachdb/pebble/internal/batchskl.(*Skiplist).node(...)
/Users/jbowens/go/src/github.com/cockroachdb/pebble/internal/batchskl/skl.go:292
github.com/cockroachdb/pebble/internal/batchskl.(*Skiplist).newNode(0xc0003af3b0, 0x1, 0x600000002, 0x6b65793100000000, 0x1)
/Users/jbowens/go/src/github.com/cockroachdb/pebble/internal/batchskl/skl.go:265 +0x16c fp=0xc00006cb60 sp=0xc00006cad0 pc=0x1742a2c
github.com/cockroachdb/pebble/internal/batchskl.(*Skiplist).Add(0xc0003af3b0, 0x0, 0x4, 0x0)
/Users/jbowens/go/src/github.com/cockroachdb/pebble/internal/batchskl/skl.go:233 +0x5fa fp=0xc00006cd88 sp=0xc00006cb60 pc=0x174202a
github.com/cockroachdb/pebble/internal/batchskl.TestBasic(0xc00014de60)
/Users/jbowens/go/src/github.com/cockroachdb/pebble/internal/batchskl/skl_test.go:161 +0x151 fp=0xc00006ced0 sp=0xc00006cd88 pc=0x1745371
testing.tRunner(0xc00014de60, 0x18a6868)
/usr/local/Cellar/go/1.14/libexec/src/testing/testing.go:992 +0x1ec fp=0xc00006cfd0 sp=0xc00006ced0 pc=0x11b613c
runtime.goexit()
/usr/local/Cellar/go/1.14/libexec/src/runtime/asm_amd64.s:1373 +0x1 fp=0xc00006cfd8 sp=0xc00006cfd0 pc=0x10a7681
created by testing.(*T).Run
/usr/local/Cellar/go/1.14/libexec/src/testing/testing.go:1043 +0x661
I think it's complaining because if we allocate a node at the end of the arena and that node has a low height in the skiplist, the bottom of the node struct will point into unallocated memory (rather than the typical allocated, but reserved for a different *node).