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Message-ID: <CAM9d7cgK-P5KuDy7hkAR4j7oB4ydE6Mw3KexqgwPPhJF6MKtXQ@mail.gmail.com>
Date: Fri, 7 Apr 2023 14:21:43 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Hangliang Lai <laihangliang1@...wei.com>
Cc: acme@...nel.org, adrian.hunter@...el.com,
alexander.shishkin@...ux.intel.com, brauner@...nel.org,
hewenliang4@...wei.com, irogers@...gle.com, jolsa@...nel.org,
linfeilong@...wei.com, linux-kernel@...r.kernel.org,
linux-perf-users@...r.kernel.org, liuwenyu7@...wei.com,
mark.rutland@....com, mingo@...hat.com, yeyunfeng@...wei.com
Subject: Re: [PATCH v2] perf top: expand the range of multithreaded phase
Hello,
On Wed, Apr 5, 2023 at 7:54 PM Hangliang Lai <laihangliang1@...wei.com> wrote:
>
> 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@...wei.com>
> Reviewed-by: Yunfeng Ye <yeyunfeng@...wei.com>
> ---
> v1 -> v2
> - Since perf top is always multi-threaded, remove top->nr_threads_synthesize judgment.
Not always, the synthesis can run in a single thread.
>
> tools/perf/builtin-top.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> index d4b5b02bab73..a18db1ee87fa 100644
> --- a/tools/perf/builtin-top.c
> +++ b/tools/perf/builtin-top.c
> @@ -1242,8 +1242,7 @@ static int __cmd_top(struct perf_top *top)
> if (perf_session__register_idle_thread(top->session) < 0)
> return ret;
>
> - if (top->nr_threads_synthesize > 1)
> - perf_set_multithreaded();
> + perf_set_multithreaded();
I think this part should be kept as is.
>
> init_process_thread(top);
>
> @@ -1273,9 +1272,6 @@ 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();
Here you can make it multi-threaded unconditionally.
Thanks,
Namhyung
> -
> if (perf_hpp_list.socket) {
> ret = perf_env__read_cpu_topology_map(&perf_env);
> if (ret < 0) {
> @@ -1352,6 +1348,9 @@ 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
>
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