linux-kernel - Re: [PATCH 08/12] perf tools: Preserve eBPF maps when loading kcore

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Message-ID: <20190522160657.GF30271@kernel.org>
Date:   Wed, 22 May 2019 13:06:57 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Stanislav Fomichev <sdf@...ichev.me>,
        Song Liu <songliubraving@...com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 08/12] perf tools: Preserve eBPF maps when loading kcore

Em Wed, May 08, 2019 at 03:20:06PM +0200, Jiri Olsa escreveu:
> We need to preserve eBPF maps even if they are
> covered by kcore, because we need to access
> eBPF dso for source data.

So, I reordered this one with the previous, as to get the output you
added to 07/12 we need what is in 08/12, and they are otherwise
completely independent, right?

- Arnaldo
 
> Adding map_groups__merge_in function to do that.
> It merges map into map_groups by splitting the
> new map within the existing map regions.
> 
> Suggested-by: Adrian Hunter <adrian.hunter@...el.com>
> Link: http://lkml.kernel.org/n/tip-mlu13e9zl6rbsz4fa00x7mfa@git.kernel.org
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  tools/perf/util/symbol.c | 97 ++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 93 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index 5cbad55cd99d..29780fcd049c 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -1166,6 +1166,85 @@ static int kcore_mapfn(u64 start, u64 len, u64 pgoff, void *data)
>  	return 0;
>  }
>  
> +/*
> + * Merges map into map_groups by splitting the new map
> + * within the existing map regions.
> + */
> +static int map_groups__merge_in(struct map_groups *kmaps, struct map *new_map)
> +{
> +	struct map *old_map;
> +	LIST_HEAD(merged);
> +
> +	for (old_map = map_groups__first(kmaps); old_map;
> +	     old_map = map_groups__next(old_map)) {
> +
> +		/* no overload with this one */
> +		if (new_map->end < old_map->start ||
> +		    new_map->start >= old_map->end)
> +			continue;
> +
> +		if (new_map->start < old_map->start) {
> +			/*
> +			 * |new......
> +			 *       |old....
> +			 */
> +			if (new_map->end < old_map->end) {
> +				/*
> +				 * |new......|     -> |new..|
> +				 *       |old....| ->       |old....|
> +				 */
> +				new_map->end = old_map->start;
> +			} else {
> +				/*
> +				 * |new.............| -> |new..|       |new..|
> +				 *       |old....|    ->       |old....|
> +				 */
> +				struct map *m = map__clone(new_map);
> +
> +				if (!m)
> +					return -ENOMEM;
> +
> +				m->end = old_map->start;
> +				list_add_tail(&m->node, &merged);
> +				new_map->start = old_map->end;
> +			}
> +		} else {
> +			/*
> +			 *      |new......
> +			 * |old....
> +			 */
> +			if (new_map->end < old_map->end) {
> +				/*
> +				 *      |new..|   -> x
> +				 * |old.........| -> |old.........|
> +				 */
> +				map__put(new_map);
> +				new_map = NULL;
> +				break;
> +			} else {
> +				/*
> +				 *      |new......| ->         |new...|
> +				 * |old....|        -> |old....|
> +				 */
> +				new_map->start = old_map->end;
> +			}
> +		}
> +	}
> +
> +	while (!list_empty(&merged)) {
> +		old_map = list_entry(merged.next, struct map, node);
> +		list_del_init(&old_map->node);
> +		map_groups__insert(kmaps, old_map);
> +		map__put(old_map);
> +	}
> +
> +	if (new_map) {
> +		map_groups__insert(kmaps, new_map);
> +		map__put(new_map);
> +	}
> +	return 0;
> +}
> +
>  static int dso__load_kcore(struct dso *dso, struct map *map,
>  			   const char *kallsyms_filename)
>  {
> @@ -1222,7 +1301,12 @@ static int dso__load_kcore(struct dso *dso, struct map *map,
>  	while (old_map) {
>  		struct map *next = map_groups__next(old_map);
>  
> -		if (old_map != 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))
>  			map_groups__remove(kmaps, old_map);
>  		old_map = next;
>  	}
> @@ -1256,11 +1340,16 @@ static int dso__load_kcore(struct dso *dso, struct map *map,
>  			map_groups__remove(kmaps, map);
>  			map_groups__insert(kmaps, map);
>  			map__put(map);
> +			map__put(new_map);
>  		} else {
> -			map_groups__insert(kmaps, new_map);
> +			/*
> +			 * Merge kcore map into existing maps,
> +			 * and ensure that current maps (eBPF)
> +			 * stay intact.
> +			 */
> +			if (map_groups__merge_in(kmaps, new_map))
> +				goto out_err;
>  		}
> -
> -		map__put(new_map);
>  	}
>  
>  	if (machine__is(machine, "x86_64")) {
> -- 
> 2.20.1

-- 

- Arnaldo