ReadMetricsSlow was updated to call the core of readMetrics on the
systemstack to prevent issues with stat skew if the stack gets moved
between readmemstats_m and readMetrics. However, readMetrics calls into
the map implementation, which has race instrumentation. The system stack
typically has no racectx set, resulting in crashes.
Donate racectx to g0 like the tracer does, so that these accesses don't
crash.
For #60607.
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-race
Change-Id: Ic0251af2d9b60361f071fe97084508223109480c
Reviewed-on: https://go-review.googlesource.com/c/go/+/539695 Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>