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Date:   Fri, 1 Feb 2019 21:07:03 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Alexei Starovoitov <ast@...nel.org>, davem@...emloft.net
Cc:     peterz@...radead.org, jannh@...gle.com, netdev@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH v7 bpf-next 0/9] introduce bpf_spin_lock

On 02/01/2019 12:40 AM, Alexei Starovoitov wrote:
> 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
> 
> v6->v7:
> - fixed this_cpu->__this_cpu per Peter's suggestion and added Ack.
> - simplified bpf_spin_lock and load/store overlap check in the verifier
>   as suggested by Andrii
> - rebase
> 
> v5->v6:
> - adopted arch_spinlock approach suggested by Peter
> - switched to spin_lock_irqsave equivalent as the simplest way
>   to avoid deadlocks in rare case of nested networking progs
>   (cgroup-bpf prog in preempt_disable vs clsbpf in softirq sharing
>   the same map with bpf_spin_lock)
>   bpf_spin_lock is only allowed in networking progs that don't
>   have arbitrary entry points unlike tracing progs.
> - rebase and split test_verifier tests
> 
> v4->v5:
> - disallow bpf_spin_lock for tracing progs due to insufficient preemption checks
> - socket filter progs cannot use bpf_spin_lock due to missing preempt_disable
> - fix atomic_set_release. Spotted by Peter.
> - fixed hash_of_maps
>   
> v3->v4:
> - fix BPF_EXIST | BPF_NOEXIST check patch 6. Spotted by Jakub. Thanks!
> - rebase
> 
> v2->v3:
> - fixed build on ia64 and archs where qspinlock is not supported
> - fixed missing lock init during lookup w/o BPF_F_LOCK. Spotted by Martin
> 
> v1->v2:
> - addressed several issues spotted by Daniel and Martin in patch 1
> - added test11 to patch 4 as suggested by Daniel
> 
> 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 verifier 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/Kconfig.locks                          |   3 +
>  kernel/bpf/arraymap.c                         |  23 +-
>  kernel/bpf/btf.c                              |  42 +++
>  kernel/bpf/core.c                             |   2 +
>  kernel/bpf/hashtab.c                          |  63 +++-
>  kernel/bpf/helpers.c                          |  96 +++++
>  kernel/bpf/local_storage.c                    |  16 +-
>  kernel/bpf/map_in_map.c                       |   5 +
>  kernel/bpf/syscall.c                          |  45 ++-
>  kernel/bpf/verifier.c                         | 171 ++++++++-
>  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                      |   1 +
>  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   | 104 +++++-
>  .../selftests/bpf/verifier/spin_lock.c        | 331 ++++++++++++++++++
>  26 files changed, 1248 insertions(+), 39 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/test_map_lock.c
>  create mode 100644 tools/testing/selftests/bpf/test_spin_lock.c
>  create mode 100644 tools/testing/selftests/bpf/verifier/spin_lock.c
> 

Applied, thanks!

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