Re: [PATCH v7 2/5] perf cpumap: Add reference count checking

[Arnaldo Carvalho de Melo]

Em Fri, Apr 07, 2023 at 04:04:02PM -0700, Ian Rogers escreveu:
> Enabled when REFCNT_CHECKING is defined. The change adds a memory
> allocated pointer that is interposed between the reference counted
> cpu map at a get and freed by a put. The pointer replaces the original
> perf_cpu_map struct, so use of the perf_cpu_map via APIs remains
> unchanged. Any use of the cpu map without the API requires two versions,
> handled via the RC_CHK_ACCESS macro.
> 
> This change is intended to catch:
>  - use after put: using a cpumap after you have put it will cause a
>    segv.
>  - unbalanced puts: two puts for a get will result in a double free
>    that can be captured and reported by tools like address sanitizer,
>    including with the associated stack traces of allocation and frees.
>  - missing puts: if a put is missing then the get turns into a memory
>    leak that can be reported by leak sanitizer, including the stack
>    trace at the point the get occurs.
> 
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> ---
>  tools/lib/perf/Makefile                  |  2 +-
>  tools/lib/perf/cpumap.c                  | 94 +++++++++++++-----------
>  tools/lib/perf/include/internal/cpumap.h |  4 +-
>  tools/perf/tests/cpumap.c                |  4 +-
>  tools/perf/util/cpumap.c                 | 40 +++++-----
>  tools/perf/util/pmu.c                    |  8 +-
>  6 files changed, 81 insertions(+), 71 deletions(-)
> 
> diff --git a/tools/lib/perf/Makefile b/tools/lib/perf/Makefile
> index d8cad124e4c5..3a9b2140aa04 100644
> --- a/tools/lib/perf/Makefile
> +++ b/tools/lib/perf/Makefile
> @@ -188,7 +188,7 @@ install_lib: libs
>  		cp -fpR $(LIBPERF_ALL) $(DESTDIR)$(libdir_SQ)
>  
>  HDRS := bpf_perf.h core.h cpumap.h threadmap.h evlist.h evsel.h event.h mmap.h
> -INTERNAL_HDRS := cpumap.h evlist.h evsel.h lib.h mmap.h threadmap.h xyarray.h
> +INTERNAL_HDRS := cpumap.h evlist.h evsel.h lib.h mmap.h rc_check.h threadmap.h xyarray.h
>  
>  INSTALL_HDRS_PFX := $(DESTDIR)$(prefix)/include/perf
>  INSTALL_HDRS := $(addprefix $(INSTALL_HDRS_PFX)/, $(HDRS))
> diff --git a/tools/lib/perf/cpumap.c b/tools/lib/perf/cpumap.c
> index 6cd0be7c1bb4..56eed1ac80d9 100644
> --- a/tools/lib/perf/cpumap.c
> +++ b/tools/lib/perf/cpumap.c
> @@ -10,16 +10,16 @@
>  #include <ctype.h>
>  #include <limits.h>
>  
> -static struct perf_cpu_map *perf_cpu_map__alloc(int nr_cpus)
> +struct perf_cpu_map *perf_cpu_map__alloc(int nr_cpus)
>  {
> -	struct perf_cpu_map *cpus = malloc(sizeof(*cpus) + sizeof(struct perf_cpu) * nr_cpus);
> -
> -	if (cpus != NULL) {
> +	struct perf_cpu_map *result;
> +	RC_STRUCT(perf_cpu_map) *cpus =
> +		malloc(sizeof(*cpus) + sizeof(struct perf_cpu) * nr_cpus);
> +	if (ADD_RC_CHK(result, cpus)) {
>  		cpus->nr = nr_cpus;
>  		refcount_set(&cpus->refcnt, 1);
> -
>  	}
> -	return cpus;
> +	return result;
>  }
>  
>  struct perf_cpu_map *perf_cpu_map__dummy_new(void)
> @@ -27,7 +27,7 @@ struct perf_cpu_map *perf_cpu_map__dummy_new(void)
>  	struct perf_cpu_map *cpus = perf_cpu_map__alloc(1);
>  
>  	if (cpus)
> -		cpus->map[0].cpu = -1;
> +		RC_CHK_ACCESS(cpus)->map[0].cpu = -1;

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