Re: [PATCH v4] perf top: expand the range of multithreaded phase

From: Arnaldo Carvalho de Melo
Date: Wed Apr 12 2023 - 09:39:35 EST


Em Tue, Apr 11, 2023 at 09:32:24AM +0800, Hangliang Lai escreveu:
> In __cmd_top, perf_set_multithreaded is used to enable pthread_rwlock, thus
> donw_read and down_write can work to handle concurrency problems. Then top
> use perf_set_singlethreaded and switch to single threaded phase, assuming
> that no thread concurrency will happen later.
> However, a UAF problem could occur in perf top in single threaded phase,
> The concurrent procedure is like this:
> display_thread process_thread
> -------------- --------------
> thread__comm_len
> -> thread__comm_str
> -> __thread__comm_str(thread)
> thread__delete
> -> comm__free
> -> comm_str__put
> -> zfree(&cs->str)
> -> thread->comm_len = strlen(comm);
> Since in single thread phase, perf_singlethreaded is true, down_read and
> down_write can not work to avoid concurrency problems.
> This patch put perf_set_singlethreaded to the function tail to expand the
> multithreaded phase range, make display_thread and process_thread run
> safe.
>
> Signed-off-by: Hangliang Lai <laihangliang1@xxxxxxxxxx>
> Co-developed-by: Wenyu Liu <liuwenyu7@xxxxxxxxxx>
> Reviewed-by: Yunfeng Ye <yeyunfeng@xxxxxxxxxx>
> Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Thanks, applied.

- Arnaldo


> ---
> v3 -> v4
> - Add Acked-by and Co-developed-by.
>
> tools/perf/builtin-top.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> index d4b5b02bab73..ae96ddaf85c4 100644
> --- a/tools/perf/builtin-top.c
> +++ b/tools/perf/builtin-top.c
> @@ -1273,8 +1273,7 @@ static int __cmd_top(struct perf_top *top)
> top->evlist->core.threads, true, false,
> top->nr_threads_synthesize);
>
> - if (top->nr_threads_synthesize > 1)
> - perf_set_singlethreaded();
> + perf_set_multithreaded();
>
> if (perf_hpp_list.socket) {
> ret = perf_env__read_cpu_topology_map(&perf_env);
> @@ -1352,6 +1351,7 @@ static int __cmd_top(struct perf_top *top)
> out_join_thread:
> cond_signal(&top->qe.cond);
> pthread_join(thread_process, NULL);
> + perf_set_singlethreaded();
> return ret;
> }
>
> --
> 2.33.0
>

--

- Arnaldo