Merge patch series "Introduce bpf_cgroup_read_xattr"

Song Liu <song@kernel.org> says:

Introduce a new kfunc bpf_cgroup_read_xattr, which can read xattr from
cgroupfs nodes. The primary users are LSMs, cgroup programs, and sched_ext.

* patches from https://lore.kernel.org/20250623063854.1896364-1-song@kernel.org:
  selftests/bpf: Add tests for bpf_cgroup_read_xattr
  bpf: Mark cgroup_subsys_state->cgroup RCU safe
  bpf: Introduce bpf_cgroup_read_xattr to read xattr of cgroup's node
  kernfs: remove iattr_mutex

Link: https://lore.kernel.org/20250623063854.1896364-1-song@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>