runtime: "found bad pointer in Go heap" on solaris-amd64-oraclerel builder

[bcmills]

2020-02-26T23:27:55-12cd55c/solaris-amd64-oraclerel

##### ../doc/codewalk
runtime: pointer 0xc00033c002 to unallocated span span.base()=0xc00033c000 span.limit=0xc00033dee0 span.state=0
runtime: found in object at *(0xc000230000+0x0)
object=0xc000230000 s.base()=0xc000230000 s.limit=0xc000232000 s.spanclass=10 s.elemsize=64 s.state=mSpanInUse
 *(object+0) = 0xc00033c002 <==
 *(object+8) = 0x9
 *(object+16) = 0xc00033c00e
 *(object+24) = 0x10
 *(object+32) = 0xc00033c021
 *(object+40) = 0xb
 *(object+48) = 0xc00033c02f
 *(object+56) = 0xc
fatal error: found bad pointer in Go heap (incorrect use of unsafe or cgo?)

The doc/codewalk test is pretty simple (no unsafe or cgo and only a little concurrency), so I suspect this is a runtime or platform bug.

Compare #35541, #32324, #28054.

CC @mknyszek, @cherrymui @aclements

[networkimprov]

Also #37506

[bcmills]

@networkimprov, I don't think there is enough evidence on #37506 to suggest a link. (For all we know, that one really could just be incorrect use of unsafe or cgo.)

[gopherbot]

Change https://golang.org/cl/227811 mentions this issue: runtime: only shrink stack while preempting