Stephen Gregoratto (original author of the fallback) says:

I read through both libcs again to compare:

Musl:
- `stat` path. Check error.
- If path is a symlink, return `OPNOTSUPP`.
- `openat` path as `O_PATH|O_NOFOLLOW|O_CLOEXEC`. Return `OPNOTSUPP` if we got `ELOOP`.
- Build procfs filename.
- `stat` procfs file.
- If procfs file is a symlink, return `OPNOTSUPP`.
- close path fd.

Glibc:
- open path as `O_PATH|O_NOFOLLOW|O_CLOEXEC`.
- fstatat path fd.
- If path is a symlink, return `OPNOTSUPP`.
- Build procfs filename.
- chmod procfs filename. Return `OPNOTSUPP` if we got `ENOENT`.
- close path fd.

I prefer glibc since you open the path first, which avoids a possible
TOCTOU race.