[v6,bpf-next,0/5] bpf: Add bpf_iter_cpumask

Message

Yafang Shao Feb. 6, 2024, 8:14 a.m. UTC

Three new kfuncs, namely bpf_iter_cpumask_{new,next,destroy}, have been
added for the new bpf_iter_cpumask functionality. These kfuncs enable the
iteration of percpu data, such as runqueues, system_group_pcpu, and more.

In our specific use case, we leverage the cgroup iterator to traverse
percpu data, subsequently exposing it to userspace through a seq file.
Refer to example in patch #2 for the usage.

Changes:
- v5 -> v6:
  - Various improvements on the comments (Andrii)
  - Use a static function instead as Kumar's patch[0] has been merged.
    (Anrii, Yonghong) 

[0]. https://lore.kernel.org/bpf/[e-mail]

- v4 -> v5:
  - Use cpumask_size() instead of sizeof(struct cpumask) (David)
  - Refactor the selftests as suggsted by David
  - Improve the doc as suggested by David
- v3 -> v4:
  - Use a copy of cpumask to avoid potential use-after-free (Yonghong)
  - Various code improvement in selftests (Yonghong)
- v2 -> v3:
  - Define KF_RCU_PROTECTED for bpf_iter_cpumask_new (Alexei)
  - Code improvement in selftests
  - Fix build error in selftest due to CONFIG_PSI=n
    reported by kernel test robot <[e-mail]>
- v1 -> v2: 
  - Avoid changing cgroup subsystem (Tejun)
  - Remove bpf_cpumask_set_from_pid(), and use bpf_cpumask_copy()
    instead (Tejun)
  - Use `int cpu;` field in bpf_iter_cpumask_kern (Andrii)

Yafang Shao (5):
  bpf: Add bpf_iter_cpumask kfuncs
  bpf, docs: Add document for cpumask iter
  selftests/bpf: Fix error checking for cpumask_success__load()
  selftests/bpf: Mark cpumask kfunc declarations as __weak
  selftests/bpf: Add selftests for cpumask iter

 Documentation/bpf/cpumasks.rst                |  60 +++++++
 kernel/bpf/cpumask.c                          |  79 +++++++++
 tools/testing/selftests/bpf/config            |   1 +
 .../selftests/bpf/prog_tests/cpumask.c        | 158 +++++++++++++++++-
 .../selftests/bpf/progs/cpumask_common.h      |  60 +++----
 .../bpf/progs/cpumask_iter_failure.c          |  99 +++++++++++
 .../bpf/progs/cpumask_iter_success.c          | 126 ++++++++++++++
 7 files changed, 552 insertions(+), 31 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/cpumask_iter_failure.c
 create mode 100644 tools/testing/selftests/bpf/progs/cpumask_iter_success.c

Comments

Andrii Nakryiko Feb. 8, 2024, 12:18 a.m. UTC | #1

On Tue, Feb 6, 2024 at 12:14 AM Yafang Shao <[e-mail]> wrote:
>
> Three new kfuncs, namely bpf_iter_cpumask_{new,next,destroy}, have been
> added for the new bpf_iter_cpumask functionality. These kfuncs enable the
> iteration of percpu data, such as runqueues, system_group_pcpu, and more.
>
> In our specific use case, we leverage the cgroup iterator to traverse
> percpu data, subsequently exposing it to userspace through a seq file.
> Refer to example in patch #2 for the usage.
>
> Changes:
> - v5 -> v6:
>   - Various improvements on the comments (Andrii)
>   - Use a static function instead as Kumar's patch[0] has been merged.
>     (Anrii, Yonghong)
>
> [0]. https://lore.kernel.org/bpf/[e-mail]
>
> - v4 -> v5:
>   - Use cpumask_size() instead of sizeof(struct cpumask) (David)
>   - Refactor the selftests as suggsted by David
>   - Improve the doc as suggested by David
> - v3 -> v4:
>   - Use a copy of cpumask to avoid potential use-after-free (Yonghong)
>   - Various code improvement in selftests (Yonghong)
> - v2 -> v3:
>   - Define KF_RCU_PROTECTED for bpf_iter_cpumask_new (Alexei)
>   - Code improvement in selftests
>   - Fix build error in selftest due to CONFIG_PSI=n
>     reported by kernel test robot <[e-mail]>
> - v1 -> v2:
>   - Avoid changing cgroup subsystem (Tejun)
>   - Remove bpf_cpumask_set_from_pid(), and use bpf_cpumask_copy()
>     instead (Tejun)
>   - Use `int cpu;` field in bpf_iter_cpumask_kern (Andrii)
>
> Yafang Shao (5):
>   bpf: Add bpf_iter_cpumask kfuncs
>   bpf, docs: Add document for cpumask iter
>   selftests/bpf: Fix error checking for cpumask_success__load()
>   selftests/bpf: Mark cpumask kfunc declarations as __weak

I've applied patches 3 and 4, as they are general clean ups and
improvements independent from the actual iterator implementation.
Thanks!

>   selftests/bpf: Add selftests for cpumask iter
>
>  Documentation/bpf/cpumasks.rst                |  60 +++++++
>  kernel/bpf/cpumask.c                          |  79 +++++++++
>  tools/testing/selftests/bpf/config            |   1 +
>  .../selftests/bpf/prog_tests/cpumask.c        | 158 +++++++++++++++++-
>  .../selftests/bpf/progs/cpumask_common.h      |  60 +++----
>  .../bpf/progs/cpumask_iter_failure.c          |  99 +++++++++++
>  .../bpf/progs/cpumask_iter_success.c          | 126 ++++++++++++++
>  7 files changed, 552 insertions(+), 31 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/progs/cpumask_iter_failure.c
>  create mode 100644 tools/testing/selftests/bpf/progs/cpumask_iter_success.c
>
> --
> 2.39.1
>