linux-kernel - Re: [PATCHv3 bpf-next 3/9] bpf: Use file object build id in stackmap

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Date:   Thu, 16 Mar 2023 15:07:31 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Hao Luo <haoluo@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Matthew Wilcox <willy@...radead.org>, bpf@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Namhyung Kim <namhyung@...il.com>,
        Dave Chinner <david@...morbit.com>
Subject: Re: [PATCHv3 bpf-next 3/9] bpf: Use file object build id in stackmap

On Thu, Mar 16, 2023 at 10:02 AM Jiri Olsa <jolsa@...nel.org> wrote:
>
> Use build id from file object in stackmap if it's available.
>
> The file's f_build_id is available (for CONFIG_FILE_BUILD_ID option)
> when the file is mmap-ed, so it will be available (if present) when
> used by stackmap.
>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---

LGTM.

Acked-by: Andrii Nakryiko <andrii@...nel.org>

>  kernel/bpf/stackmap.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
> index 0f1d8dced933..14d27bd83081 100644
> --- a/kernel/bpf/stackmap.c
> +++ b/kernel/bpf/stackmap.c
> @@ -124,6 +124,28 @@ static struct bpf_map *stack_map_alloc(union bpf_attr *attr)
>         return ERR_PTR(err);
>  }
>
> +#ifdef CONFIG_FILE_BUILD_ID
> +static int vma_get_build_id(struct vm_area_struct *vma, unsigned char *build_id)
> +{
> +       struct build_id *bid;
> +
> +       if (!vma->vm_file)
> +               return -EINVAL;
> +       bid = vma->vm_file->f_build_id;
> +       if (IS_ERR_OR_NULL(bid))
> +               return bid ? PTR_ERR(bid) : -ENOENT;
> +       if (bid->sz > BUILD_ID_SIZE_MAX)
> +               return -EINVAL;
> +       memcpy(build_id, bid->data, bid->sz);
> +       return 0;
> +}
> +#else
> +static int vma_get_build_id(struct vm_area_struct *vma, unsigned char *build_id)
> +{
> +       return build_id_parse(vma, build_id, NULL);
> +}
> +#endif
> +
>  static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
>                                           u64 *ips, u32 trace_nr, bool user)
>  {
> @@ -156,7 +178,7 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
>                         goto build_id_valid;
>                 }
>                 vma = find_vma(current->mm, ips[i]);
> -               if (!vma || build_id_parse(vma, id_offs[i].build_id, NULL)) {
> +               if (!vma || vma_get_build_id(vma, id_offs[i].build_id)) {
>                         /* per entry fall back to ips */
>                         id_offs[i].status = BPF_STACK_BUILD_ID_IP;
>                         id_offs[i].ip = ips[i];
> --
> 2.39.2
>