netdev - Re: [PATCH bpf-next v1 2/5] cgroup: bpf: add cgroup_rstat_updated() and cgroup_rstat

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Date:   Fri, 20 May 2022 09:20:07 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Yonghong Song <yhs@...com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shuah Khan <shuah@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Michal Hocko <mhocko@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH bpf-next v1 2/5] cgroup: bpf: add cgroup_rstat_updated()
 and cgroup_rstat_flush() kfuncs

On Fri, May 20, 2022 at 9:16 AM Yonghong Song <yhs@...com> wrote:
>
>
>
> On 5/20/22 9:08 AM, Yosry Ahmed wrote:
> > On Fri, May 20, 2022 at 8:15 AM Yonghong Song <yhs@...com> wrote:
> >>
> >>
> >>
> >> On 5/19/22 6:21 PM, Yosry Ahmed wrote:
> >>> Add cgroup_rstat_updated() and cgroup_rstat_flush() kfuncs to bpf
> >>> tracing programs. bpf programs that make use of rstat can use these
> >>> functions to inform rstat when they update stats for a cgroup, and when
> >>> they need to flush the stats.
> >>>
> >>> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
> >>> ---
> >>>    kernel/cgroup/rstat.c | 35 ++++++++++++++++++++++++++++++++++-
> >>>    1 file changed, 34 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
> >>> index e7a88d2600bd..a16a851bc0a1 100644
> >>> --- a/kernel/cgroup/rstat.c
> >>> +++ b/kernel/cgroup/rstat.c
> >>> @@ -3,6 +3,11 @@
> >>>
> >>>    #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);
> >>>
> >>> @@ -141,7 +146,12 @@ 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 */
> >>> +/*
> >>> + * 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.
> >>> + */
> >>>    __weak noinline void bpf_rstat_flush(struct cgroup *cgrp,
> >>>                                     struct cgroup *parent, int cpu)
> >>>    {
> >>> @@ -476,3 +486,26 @@ 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_SET_START(bpf_rstat_check_kfunc_ids)
> >>> +BTF_ID(func, cgroup_rstat_updated)
> >>> +BTF_ID(func, cgroup_rstat_flush)
> >>> +BTF_SET_END(bpf_rstat_check_kfunc_ids)
> >>> +
> >>> +BTF_SET_START(bpf_rstat_sleepable_kfunc_ids)
> >>> +BTF_ID(func, cgroup_rstat_flush)
> >>> +BTF_SET_END(bpf_rstat_sleepable_kfunc_ids)
> >>> +
> >>> +static const struct btf_kfunc_id_set bpf_rstat_kfunc_set = {
> >>> +     .owner          = THIS_MODULE,
> >>> +     .check_set      = &bpf_rstat_check_kfunc_ids,
> >>> +     .sleepable_set  = &bpf_rstat_sleepable_kfunc_ids,
> >>
> >> There is a compilation error here:
> >>
> >> kernel/cgroup/rstat.c:503:3: error: ‘const struct btf_kfunc_id_set’ has
> >> no member named ‘sleepable_set’; did you mean ‘release_set’?
> >>       503 |  .sleepable_set = &bpf_rstat_sleepable_kfunc_ids,
> >>           |   ^~~~~~~~~~~~~
> >>           |   release_set
> >>     kernel/cgroup/rstat.c:503:19: warning: excess elements in struct
> >> initializer
> >>       503 |  .sleepable_set = &bpf_rstat_sleepable_kfunc_ids,
> >>           |                   ^
> >>     kernel/cgroup/rstat.c:503:19: note: (near initialization for
> >> ‘bpf_rstat_kfunc_set’)
> >>     make[3]: *** [scripts/Makefile.build:288: kernel/cgroup/rstat.o] Error 1
> >>
> >> Please fix.
> >
> > This patch series is rebased on top of 2 patches in the mailing list:
> > - bpf/btf: also allow kfunc in tracing and syscall programs
> > - btf: Add a new kfunc set which allows to mark a function to be
> >    sleepable
> >
> > I specified this in the cover letter, do I need to do something else
> > in this situation? Re-send the patches as part of my series?
>
> At least put a link in the cover letter for the above two patches?
> This way, people can easily find them to double check.

Right. Will do this in the next version. Sorry for the inconvenience.

>
> >
> >
> >
> >>
> >>> +};
> >>> +
> >>> +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);