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From:   Namhyung Kim <namhyung@kernel.org>
Date:   Mon, 4 Dec 2023 15:49:45 -0800
Message-ID: <CAM9d7cgj4Wj+0ZFQ3XfG12kkp4ThE4RT1+g=A1aSOinCXM9w+Q@mail.gmail.com>
Subject: Re: [PATCH v5 16/50] perf maps: Add remove maps function to remove a
 map based on callback
To:     Ian Rogers <irogers@google.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
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        Kan Liang <kan.liang@linux.intel.com>,
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        Huacai Chen <chenhuacai@kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Vincent Whitchurch <vincent.whitchurch@axis.com>,
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        Sandipan Das <sandipan.das@amd.com>,
        liuwenyu <liuwenyu7@huawei.com>, linux-kernel@vger.kernel.org,
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On Mon, Nov 27, 2023 at 2:10 PM Ian Rogers <irogers@google.com> wrote:
>
> Removing maps wasn't being done under the write lock. Similar to
> maps__for_each_map, iterate the entries but in this case remove the
> entry based on the result of the callback. If an entry was removed
> then maps_by_name also needs updating, so add missed flush.
>
> In dso__load_kcore, the test of map to save would always be false with
> REFCNT_CHECKING because of a missing RC_CHK_ACCESS.
>
> Signed-off-by: Ian Rogers <irogers@google.com>

Acked-by: Namhyung Kim <namhyung@kernel.org>

A nitpick below,

> ---
[SNIP]
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index 72f03b875478..30da8a405d11 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -1239,13 +1239,23 @@ static int kcore_mapfn(u64 start, u64 len, u64 pgoff, void *data)
>         return 0;
>  }
>
> +static bool remove_old_maps(struct map *map, void *data)
> +{
> +       const struct map *map_to_save = data;
> +
> +       /*
> +        * We need to preserve eBPF maps even if they are covered by kcore,
> +        * because we need to access eBPF dso for source data.
> +        */
> +       return RC_CHK_ACCESS(map) != RC_CHK_ACCESS(map_to_save) && !__map__is_bpf_prog(map);

RC_CHK_EQUAL(map, map_to_save) ?

Thanks,
Namhyung


> +}
> +
>  static int dso__load_kcore(struct dso *dso, struct map *map,
>                            const char *kallsyms_filename)
>  {
>         struct maps *kmaps = map__kmaps(map);
>         struct kcore_mapfn_data md;
>         struct map *replacement_map = NULL;
> -       struct map_rb_node *old_node, *next;
>         struct machine *machine;
>         bool is_64_bit;
>         int err, fd;
> @@ -1292,17 +1302,7 @@ static int dso__load_kcore(struct dso *dso, struct map *map,
>         }
>
>         /* Remove old maps */
> -       maps__for_each_entry_safe(kmaps, old_node, next) {
> -               struct map *old_map = old_node->map;
> -
> -               /*
> -                * We need to preserve eBPF maps even if they are
> -                * covered by kcore, because we need to access
> -                * eBPF dso for source data.
> -                */
> -               if (old_map != map && !__map__is_bpf_prog(old_map))
> -                       maps__remove(kmaps, old_map);
> -       }
> +       maps__remove_maps(kmaps, remove_old_maps, map);
>         machine->trampolines_mapped = false;
>
>         /* Find the kernel map using the '_stext' symbol */
> --
> 2.43.0.rc1.413.gea7ed67945-goog
>