[PATCH v3 0/4] cgroup: expose cpu.stat and io.stat to BPF

[Ziyang Men <ziyang.meme@gmail.com>]

Collecting cgroup statistics is expensive: the existing method is to
open and parse a cgroup file for every cgroup of interest. The memory
controller already has an efficient alternative through BPF; this series
extends that model to the CPU and block I/O controllers.

Patch 1 adds the CPU kfuncs, and patch 2 adds their selftest. Patch 3
adds the blkcg kfuncs, and patch 4 adds their selftest.

This v3 combines the two previously posted v2 series:
CPU v2: https://lore.kernel.org/all/20260818002450.3071325-1-ziyang.meme@gmail.com/
blkcg v2: https://lore.kernel.org/all/20260817214205.723267-1-ziyang.meme@gmail.com/

===
Changes since CPU v2:
- Rename bpf_cpu.c to bpf_cgroup.c and use unlikely() and container_of()
  for the task_group conversion.
- Remove bpf_css_flush_rstat() and register the existing
  css_rstat_flush() in the common kfunc set.
- Remove the SLEEPABLE mark bpf_cgroup_base_stat().

Changes since blkcg v2:
- Add bpf_cgroup_css() and bpf_css_release() to keep a controller css
  alive across the sleepable rstat flush.
- Add an RCU-protected checked css-to-blkcg conversion and make the blkg
  iterator take the typed blkcg pointer.
- Use the existing css_rstat_flush() and remove bpf_blkcg_flush_stats().
- Do not expose root io.stat values.

===
Changes since CPU v1:
- Make the rstat flush generic, move it to rstat.c, and make it take a css.
- Expose cgroup_base_stat directly instead of repacking its CPU times.
- Replace the throttled-time aggregation kfunc with a checked RCU cast in
  the CPU cgroup BPF code. The cast preserves the verifier type needed for
  the BPF program to perform the per-CPU sum itself.
- Remove the scheduler changes.

Built with LLVM. Pass test on v7.2-rc5.

Ziyang Men (4):
  cgroup: add BPF kfuncs to read a cpu cgroup's stats
  selftests/bpf: add cgroup_iter_cpu test for cpu cgroup kfuncs
  block: add BPF kfuncs to read blkcg io.stat
  selftests/bpf: add test for blkcg io.stat BPF kfuncs

 MAINTAINERS                                   |   1 +
 block/Makefile                                |   3 +
 block/bpf_blkcg.c                             | 138 ++++++++++
 kernel/cgroup/Makefile                        |   2 +
 kernel/cgroup/bpf_cgroup.c                    | 100 +++++++
 kernel/cgroup/rstat.c                         |  54 +++-
 tools/testing/selftests/bpf/cgroup_iter_cpu.h |  22 ++
 tools/testing/selftests/bpf/cgroup_iter_io.h  |  17 ++
 tools/testing/selftests/bpf/config            |   4 +
 .../bpf/prog_tests/cgroup_iter_cpu.c          | 259 ++++++++++++++++++
 .../selftests/bpf/prog_tests/cgroup_iter_io.c | 254 +++++++++++++++++
 .../selftests/bpf/progs/cgroup_iter_cpu.c     | 113 ++++++++
 .../selftests/bpf/progs/cgroup_iter_io.c      |  74 +++++
 13 files changed, 1037 insertions(+), 4 deletions(-)
 create mode 100644 block/bpf_blkcg.c
 create mode 100644 kernel/cgroup/bpf_cgroup.c
 create mode 100644 tools/testing/selftests/bpf/cgroup_iter_cpu.h
 create mode 100644 tools/testing/selftests/bpf/cgroup_iter_io.h
 create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_iter_cpu.c
 create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_iter_io.c
 create mode 100644 tools/testing/selftests/bpf/progs/cgroup_iter_cpu.c
 create mode 100644 tools/testing/selftests/bpf/progs/cgroup_iter_io.c


base-commit: 3b5f4b83c4abc0c9b0a7b9e2b44e816611b7f2ec
-- 
2.53.0-Meta