Re: [PATCH v5 02/50] libperf: Lazily allocate/size mmap event copy

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Mon, Nov 27, 2023 at 02:08:14PM -0800, Ian Rogers escreveu:
> The event copy in the mmap is used to have storage to read an
> event. Not all users of mmaps read the events, such as perf
> record. The amount of buffer was also statically set to
> PERF_SAMPLE_MAX_SIZE rather than the amount necessary from the
> header's event size. Switch to a model where the event_copy is
> reallocated if too small to the event's size. This adds the potential
> for the event to move, so if a copy of the event pointer were stored
> it could be broken. All the current users do:
> 
>   while(event = perf_mmap__read_event()) { ... }
> 
> and so they would be broken due to the event being overwritten if they
> had stored the pointer. Manual inspection and address sanitizer
> testing also shows the event pointer not being stored.
> 
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/lib/perf/include/internal/mmap.h |  3 ++-
>  tools/lib/perf/mmap.c                  | 21 ++++++++++++++++++---
>  2 files changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/lib/perf/include/internal/mmap.h b/tools/lib/perf/include/internal/mmap.h
> index 5a062af8e9d8..5f08cab61ece 100644
> --- a/tools/lib/perf/include/internal/mmap.h
> +++ b/tools/lib/perf/include/internal/mmap.h
> @@ -33,7 +33,8 @@ struct perf_mmap {
>  	bool			 overwrite;
>  	u64			 flush;
>  	libperf_unmap_cb_t	 unmap_cb;
> -	char			 event_copy[PERF_SAMPLE_MAX_SIZE] __aligned(8);
> +	void			*event_copy;
> +	size_t			 event_copy_sz;
>  	struct perf_mmap	*next;
>  };
>  
> diff --git a/tools/lib/perf/mmap.c b/tools/lib/perf/mmap.c
> index 2184814b37dd..c829db7bf1fa 100644
> --- a/tools/lib/perf/mmap.c
> +++ b/tools/lib/perf/mmap.c
> @@ -19,6 +19,7 @@
>  void perf_mmap__init(struct perf_mmap *map, struct perf_mmap *prev,
>  		     bool overwrite, libperf_unmap_cb_t unmap_cb)
>  {
> +	/* Assume fields were zero initialized. */
>  	map->fd = -1;
>  	map->overwrite = overwrite;
>  	map->unmap_cb  = unmap_cb;
> @@ -51,13 +52,19 @@ int perf_mmap__mmap(struct perf_mmap *map, struct perf_mmap_param *mp,
>  
>  void perf_mmap__munmap(struct perf_mmap *map)
>  {
> -	if (map && map->base != NULL) {
> +	if (!map)
> +		return;
> +
> +	free(map->event_copy);
> +	map->event_copy = NULL;

I´m converting this to:

	zfree(&map->event_copy);

Hopefully we'll find some tool to flag these before submitting patches,
does clang-tidy do these kinds of things?

Also, applied:

 b4 am -P2,4-7 -ctsl --cc-trailers 20231127220902.1315692-1-irogers@google.com

The ones that Namhyung acked and that applied cleanly in order.

The first one, as Namhyung noted, is already merged.

- Arnaldo