netdev - Re: [PATCH v2 bpf-next 0/9] introduce bpf_spin

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Date:   Tue, 22 Jan 2019 15:34:11 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Network Development <netdev@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 0/9] introduce bpf_spin_lock

On Thu, Jan 17, 2019 at 10:14 PM Alexei Starovoitov <ast@...nel.org> 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
>
> v1->v2:
> - addressed several issues spotted by Daniel and Martin in patch 1
> - added test11 to patch 4 as suggested by Daniel

Found a build error on ia64 when SMP is on, but qspinlock
is not used.
Will be respining the set.