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

[Nuo Mi <nuomi2021@gmail.com>]

On Thu, Jul 11, 2024 at 8:21 PM Nuo Mi <nuomi2021@gmail.com> wrote:

>
>
> On Wed, Jul 10, 2024 at 5:14 PM Anton Khirnov <anton@khirnov.net> wrote:
>
>> Quoting Nuo Mi (2024-07-09 13:36:09)
>> > On Tue, Jul 9, 2024 at 6:35 AM Timo Rothenpieler <timo@rothenpieler.org
>> >
>> > wrote:
>> >
>> > > On 08.07.2024 17:32, Zhao Zhili wrote:
>> > > >
>> > > >
>> > > >> On Jul 8, 2024, at 22:07, Timo Rothenpieler <timo@rothenpieler.org
>> >
>> > > wrote:
>> > > >>
>> > > >> On 08.07.2024 09:43, Zhao Zhili wrote:
>> > > >>> From: Zhao Zhili <zhilizhao@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.
>>
> Editors will highlight the comment with green too, which will help protect
> our eyes.
>
Applied.
Thank you, for the patch and review.


>> --
>> Anton Khirnov
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>
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