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    Subject[PATCH bpf-next v6 6/8] cgroup: bpf: enable bpf programs to integrate with rstat
    From
    From: Yosry Ahmed <yosryahmed@google.com>

    From: Yosry Ahmed <yosryahmed@google.com>

    Enable bpf programs to make use of rstat to collect cgroup hierarchical
    stats efficiently:
    - Add cgroup_rstat_updated() kfunc, for bpf progs that collect stats.
    - Add cgroup_rstat_flush() sleepable kfunc, for bpf progs that read stats.
    - Add an empty bpf_rstat_flush() hook that is called during rstat
    flushing, for bpf progs that flush stats to attach to. Attaching a bpf
    prog to this hook effectively registers it as a flush callback.

    Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
    Acked-by: Tejun Heo <tj@kernel.org>
    Signed-off-by: Hao Luo <haoluo@google.com>
    ---
    kernel/cgroup/rstat.c | 48 +++++++++++++++++++++++++++++++++++++++++++
    1 file changed, 48 insertions(+)

    diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
    index 24b5c2ab5598..3289f6e0d306 100644
    --- a/kernel/cgroup/rstat.c
    +++ b/kernel/cgroup/rstat.c
    @@ -3,6 +3,10 @@

    #include <linux/sched/cputime.h>

    +#include <linux/bpf.h>
    +#include <linux/btf.h>
    +#include <linux/btf_ids.h>
    +
    static DEFINE_SPINLOCK(cgroup_rstat_lock);
    static DEFINE_PER_CPU(raw_spinlock_t, cgroup_rstat_cpu_lock);

    @@ -141,6 +145,31 @@ static struct cgroup *cgroup_rstat_cpu_pop_updated(struct cgroup *pos,
    return pos;
    }

    +/*
    + * A hook for bpf stat collectors to attach to and flush their stats.
    + * Together with providing bpf kfuncs for cgroup_rstat_updated() and
    + * cgroup_rstat_flush(), this enables a complete workflow where bpf progs that
    + * collect cgroup stats can integrate with rstat for efficient flushing.
    + *
    + * A static noinline declaration here could cause the compiler to optimize away
    + * the function. A global noinline declaration will keep the definition, but may
    + * optimize away the callsite. Therefore, __weak is needed to ensure that the
    + * call is still emitted, by telling the compiler that we don't know what the
    + * function might eventually be.
    + *
    + * __diag_* below are needed to dismiss the missing prototype warning.
    + */
    +__diag_push();
    +__diag_ignore_all("-Wmissing-prototypes",
    + "kfuncs which will be used in BPF programs");
    +
    +__weak noinline void bpf_rstat_flush(struct cgroup *cgrp,
    + struct cgroup *parent, int cpu)
    +{
    +}
    +
    +__diag_pop();
    +
    /* see cgroup_rstat_flush() */
    static void cgroup_rstat_flush_locked(struct cgroup *cgrp, bool may_sleep)
    __releases(&cgroup_rstat_lock) __acquires(&cgroup_rstat_lock)
    @@ -168,6 +197,7 @@ static void cgroup_rstat_flush_locked(struct cgroup *cgrp, bool may_sleep)
    struct cgroup_subsys_state *css;

    cgroup_base_stat_flush(pos, cpu);
    + bpf_rstat_flush(pos, cgroup_parent(pos), cpu);

    rcu_read_lock();
    list_for_each_entry_rcu(css, &pos->rstat_css_list,
    @@ -469,3 +499,21 @@ void cgroup_base_stat_cputime_show(struct seq_file *seq)
    "system_usec %llu\n",
    usage, utime, stime);
    }
    +
    +/* Add bpf kfuncs for cgroup_rstat_updated() and cgroup_rstat_flush() */
    +BTF_SET8_START(bpf_rstat_kfunc_ids)
    +BTF_ID_FLAGS(func, cgroup_rstat_updated)
    +BTF_ID_FLAGS(func, cgroup_rstat_flush, KF_SLEEPABLE)
    +BTF_SET8_END(bpf_rstat_kfunc_ids)
    +
    +static const struct btf_kfunc_id_set bpf_rstat_kfunc_set = {
    + .owner = THIS_MODULE,
    + .set = &bpf_rstat_kfunc_ids,
    +};
    +
    +static int __init bpf_rstat_kfunc_init(void)
    +{
    + return register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING,
    + &bpf_rstat_kfunc_set);
    +}
    +late_initcall(bpf_rstat_kfunc_init);
    --
    2.37.1.455.g008518b4e5-goog
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