From: Hou Tao <houtao1@xxxxxxxxxx>
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@xxxxxxxxxxxxxxx/
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
--
2.29.2
