crypto/internal/fips140/drbg: remove global lock

[rsc]

There is still a global lock in the drbg package, so that crypto/rand.Read during fips mode will have significantly more contention than without. Worse, the code is inside the fips140 boundary, meaning it will take years for any change made after the release to be recertified and propagate out into actual (fips140) usage.

I believe we should change the drbg state to be per-P, before the release. This only affects the fips140 code path, not ordinary programs running in the default (non-fips140) mode, so it should be fairly low risk.

I will look into doing this.

/cc @FiloSottile

[gopherbot]

Change https://go.dev/cl/641097 mentions this issue: crypto/internal/fips140/drbg: avoid global lock on rand state