Subject: [PATCH bpf-next 0/9] introduce bpf_spin_lock

From: Alexei Starovoitov <[email-masked]>
Date: Tue, 15 Jan 2019 21:08:21 -0800

Many algorithms need to read and modify several variables atomically.
Until now it was hard to impossible to implement such algorithms in BPF.
Hence introduce support for bpf_spin_lock.

The api consists of 'struct bpf_spin_lock' that should be placed
inside hash/array/cgroup_local_storage element
and bpf_spin_lock/unlock() helper function.

Example:
struct hash_elem {
    int cnt;
    struct bpf_spin_lock lock;
};
struct hash_elem * val = bpf_map_lookup_elem(&hash_map, &key);
if (val) {
    bpf_spin_lock(&val->lock);
    val->cnt++;
    bpf_spin_unlock(&val->lock);
}

and BPF_F_LOCK flag for lookup/update bpf syscall commands that
allows user space to read/write map elements under lock.

Together these primitives allow race free access to map elements
from bpf programs and from user space.

Key restriction: root only.
Key requirement: maps must be annotated with BTF.

This concept was discussed at Linux Plumbers Conference 2018.
Thank you everyone who participated and helped to iron out details
of api and implementation.

Patch 1: bpf_spin_lock support in the verifier, BTF, hash, array.
Patch 2: bpf_spin_lock in cgroup local storage.
Patches 3,4,5: tests
Patch 6: BPF_F_LOCK flag to lookup/update
Patches 7,8,9: tests

Alexei Starovoitov (9):
  bpf: introduce bpf_spin_lock
  bpf: add support for bpf_spin_lock to cgroup local storage
  tools/bpf: sync include/uapi/linux/bpf.h
  selftests/bpf: add bpf_spin_lock tests
  selftests/bpf: add bpf_spin_lock C test
  bpf: introduce BPF_F_LOCK flag
  tools/bpf: sync uapi/bpf.h
  libbpf: introduce bpf_map_lookup_elem_flags()
  selftests/bpf: test for BPF_F_LOCK

 include/linux/bpf.h                          |  39 +-
 include/linux/bpf_verifier.h                 |   1 +
 include/linux/btf.h                          |   1 +
 include/uapi/linux/bpf.h                     |   8 +-
 kernel/bpf/arraymap.c                        |  23 +-
 kernel/bpf/btf.c                             |  37 ++
 kernel/bpf/core.c                            |   2 +
 kernel/bpf/hashtab.c                         |  48 ++-
 kernel/bpf/helpers.c                         |  53 +++
 kernel/bpf/local_storage.c                   |  16 +-
 kernel/bpf/syscall.c                         |  48 ++-
 kernel/bpf/verifier.c                        | 139 +++++-
 net/core/filter.c                            |  16 +-
 tools/include/uapi/linux/bpf.h               |   8 +-
 tools/lib/bpf/bpf.c                          |  13 +
 tools/lib/bpf/bpf.h                          |   2 +
 tools/lib/bpf/libbpf.map                     |   4 +
 tools/lib/bpf/tags                           | 254 +++++++++++
 tools/testing/selftests/bpf/Makefile         |   2 +-
 tools/testing/selftests/bpf/bpf_helpers.h    |   4 +
 tools/testing/selftests/bpf/test_map_lock.c  |  66 +++
 tools/testing/selftests/bpf/test_progs.c     | 117 ++++-
 tools/testing/selftests/bpf/test_spin_lock.c | 108 +++++
 tools/testing/selftests/bpf/test_verifier.c  | 429 ++++++++++++++++++-
 24 files changed, 1411 insertions(+), 27 deletions(-)
 create mode 100644 tools/lib/bpf/tags
 create mode 100644 tools/testing/selftests/bpf/test_map_lock.c
 create mode 100644 tools/testing/selftests/bpf/test_spin_lock.c

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2.17.1