[FFmpeg-devel] [PATCH 2/2] avutil/executor: Fix stack overflow due to recursive call

[Anton Khirnov]

Quoting Nuo Mi (2024-07-09 13:36:09)
> On Tue, Jul 9, 2024 at 6:35 AM Timo Rothenpieler <timo at rothenpieler.org>
> wrote:
> 
> > On 08.07.2024 17:32, Zhao Zhili wrote:
> > >
> > >
> > >> On Jul 8, 2024, at 22:07, Timo Rothenpieler <timo at rothenpieler.org>
> > wrote:
> > >>
> > >> On 08.07.2024 09:43, Zhao Zhili wrote:
> > >>> From: Zhao Zhili <zhilizhao at tencent.com>
> > >>> av_executor_execute run the task directly when thread is disabled.
> > >>> The task can schedule a new task by call av_executor_execute. This
> > >>> forms an implicit recursive call. This patch removed the recursive
> > >>> call.
> > >>> ---
> > >>>   libavutil/executor.c | 5 +++++
> > >>>   1 file changed, 5 insertions(+)
> > >>> diff --git a/libavutil/executor.c b/libavutil/executor.c
> > >>> index 89058fab2f..c145c51be9 100644
> > >>> --- a/libavutil/executor.c
> > >>> +++ b/libavutil/executor.c
> > >>> @@ -58,6 +58,7 @@ struct AVExecutor {
> > >>>       int die;
> > >>>         AVTask *tasks;
> > >>> +    int stack_depth;
> > >>>   };
> > >>>     static AVTask* remove_task(AVTask **prev, AVTask *t)
> > >>> @@ -207,8 +208,12 @@ void av_executor_execute(AVExecutor *e, AVTask *t)
> > >>>       }
> > >>>         if (!e->thread_count || !HAVE_THREADS) {
> > >>> +        if (e->stack_depth > 0)
> > >>> +            return;
> > >>> +        e->stack_depth++;
> > >>>           // We are running in a single-threaded environment, so we
> > must handle all tasks ourselves
> > >>>           while (run_one_task(e, e->local_contexts))
> > >>>               /* nothing */;
> > >>> +        e->stack_depth--;
> > >>
> > >> Won't this put the above line into the "nothing" while-loop?
> > >> Is that intended? If so, the indentation should be adjusted accordingly.
> > >> If not, the while-loop should gain empty {}.
> > >
> > > The comment specify it’s a while loop with empty body. Maybe it’s not
> > obvious
> > > in the email client.
> >
> > Oh, there is a ; behind the comment.
> > Completely missed that. Can't say I like it, but yeah, that works.
> >
> Google suggests using "while (cond) continue;":
> https://google.github.io/styleguide/cppguide.html#Formatting_Looping_Branching
> .
> However, it's not better than using /* nothing */.

continue gets hilit by your editor.

Also, I'd put it on a separate line for extra visibility.

And bikesheds should be black with red stripes.

-- 
Anton Khirnov