[PATCH bpf-next v2 0/4] Use this_cpu_xxx for preemption-safety

From: Hou Tao <houtao@huaweicloud.com>
To: bpf@vger.kernel.org
Cc: Song Liu <songliubraving@fb.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Hao Sun <sunhao.th@gmail.com>, Hao Luo <haoluo@google.com>,
	Andrii Nakryiko <andrii@kernel.org>, Yonghong Song <yhs@fb.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, KP Singh <kpsingh@kernel.org>,
	"David S . Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Stanislav Fomichev <sdf@google.com>, Jiri Olsa <jolsa@kernel.org>,
	John Fastabend <john.fastabend@gmail.com>,
	Lorenz Bauer <oss@lmb.io>,
	houtao1@huawei.com
Subject: [PATCH bpf-next v2 0/4] Use this_cpu_xxx for preemption-safety
Date: Thu,  1 Sep 2022 14:19:34 +0800	[thread overview]
Message-ID: <20220901061938.3789460-1-houtao@huaweicloud.com> (raw)

From: Hou Tao <houtao1@huawei.com>

Hi,

The patchset aims to make the update of per-cpu prog->active and per-cpu
bpf_task_storage_busy being preemption-safe. The problem is on same
architectures (e.g. arm64), __this_cpu_{inc|dec|inc_return} are neither
preemption-safe nor IRQ-safe, so under fully preemptible kernel the
concurrent updates on these per-cpu variables may be interleaved and the
final values of these variables may be not zero.

Patch 1 & 2 use the preemption-safe per-cpu helpers to manipulate
prog->active and bpf_task_storage_busy. Patch 3 & 4 add a test case in
map_tests to show the concurrent updates on the per-cpu
bpf_task_storage_busy by using __this_cpu_{inc|dec} are not atomic.

Comments are always welcome.

Regards,
Tao

Change Log:
v2:
* Patch 1: update commit message to indicate the problem is only
  possible for fully preemptible kernel
* Patch 2: a new patch which fixes the problem for prog->active
* Patch 3 & 4: move it to test_maps and make it depend on CONFIG_PREEMPT

v1: https://lore.kernel.org/bpf/20220829142752.330094-1-houtao@huaweicloud.com/

Hou Tao (4):
  bpf: Use this_cpu_{inc|dec|inc_return} for bpf_task_storage_busy
  bpf: Use this_cpu_{inc_return|dec} for prog->active
  selftests/bpf: Move sys_pidfd_open() into task_local_storage_helpers.h
  selftests/bpf: Test concurrent updates on bpf_task_storage_busy

 kernel/bpf/bpf_local_storage.c                |   4 +-
 kernel/bpf/bpf_task_storage.c                 |   8 +-
 kernel/bpf/trampoline.c                       |   8 +-
 .../bpf/map_tests/task_storage_map.c          | 122 ++++++++++++++++++
 .../selftests/bpf/prog_tests/test_bprm_opts.c |  10 +-
 .../bpf/prog_tests/test_local_storage.c       |  10 +-
 .../bpf/progs/read_bpf_task_storage_busy.c    |  39 ++++++
 .../bpf/task_local_storage_helpers.h          |  18 +++
 8 files changed, 191 insertions(+), 28 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/map_tests/task_storage_map.c
 create mode 100644 tools/testing/selftests/bpf/progs/read_bpf_task_storage_busy.c
 create mode 100644 tools/testing/selftests/bpf/task_local_storage_helpers.h

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2.29.2