Re: [PATCH] perf top: add concurrent access protection of the SLsmg screen management

[Jiri Olsa]

On Wed, Dec 29, 2021 at 04:55:19PM +0800, yaowenbin wrote:
> When the following command is executed several times, a coredump file is generated.
> 	$ timeout -k 9 5 perf top -e task-clock
> 	*******
> 	*******
> 	*******
> 	0.01%  [kernel]                  [k] __do_softirq
> 	0.01%  libpthread-2.28.so        [.] __pthread_mutex_lock
> 	0.01%  [kernel]                  [k] __ll_sc_atomic64_sub_return
> 	double free or corruption (!prev) perf top --sort comm,dso
> 	timeout: the monitored command dumped core
> 
> When we terminate "perf top" using sending signal method, SLsmg_reset_smg
> function is called. SLsmg_reset_smg resets the SLsmg screen management routines
> by freeing all memory allocated while it was active. However SLsmg_reinit_smg
> function maybe be called by another thread. SLsmg_reinit_smg function will
> free the same memory accessed by SLsmg_reset_smg functon, thus it results
> in double free. SLsmg_reinit_smg function is called already protected by
> ui__lock, so we fix the problem by adding pthread_mutex_trylock of ui__lock
> when calling SLsmg_reset_smg function.
> 
> Signed-off-by: yaowenbin <yaowenbin1@xxxxxxxxxx>
> Signed-off-by: hewenliang <hewenliang4@xxxxxxxxxx>
> Signed-off-by: Wenyu Liu <liuwenyu7@xxxxxxxxxx>
> ---
>  tools/perf/ui/tui/setup.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/perf/ui/tui/setup.c b/tools/perf/ui/tui/setup.c
> index d4ac41679..1fdf92062 100644
> --- a/tools/perf/ui/tui/setup.c
> +++ b/tools/perf/ui/tui/setup.c
> @@ -170,9 +170,11 @@ void ui__exit(bool wait_for_ok)
>  				    "Press any key...", 0);
> 
>  	SLtt_set_cursor_visibility(1);
> -	SLsmg_refresh();
> -	SLsmg_reset_smg();
> +	if (!pthread_mutex_trylock(&ui__lock)) {

trylock because it can be called from signal, right?
could you plase add some comment about that

thanks,
jirka

> +		SLsmg_refresh();
> +		SLsmg_reset_smg();
> +		pthread_mutex_unlock(&ui__lock);
> +	}
>  	SLang_reset_tty();
> -
>  	perf_error__unregister(&perf_tui_eops);
>  }
> --
> 2.27.0
>