On Mon, 19 Jun 2023 12:44:06 +0200
Christian König <christian.koenig@xxxxxxx> wrote:
> Am 19.06.23 um 12:12 schrieb Boris Brezillon:
> > [SNIP]
> > Note that the drm_exec_until_all_locked() helper I introduced is taking
> > an expression, so in theory, you don't have to define a separate
> > function.
> >
> > drm_exec_until_all_locked(&exec, {
> > /* inlined-code */
> > int ret;
> >
> > ret = blabla()
> > if (ret)
> > goto error;
> >
> > ...
> >
> > error:
> > /* return value. */
> > ret;
> > });
> >
> > This being said, as soon as you have several failure paths,
> > it makes things a lot easier/controllable if you make it a function,
> > and I honestly don't think the readability would suffer from having a
> > function defined just above the user. My main concern with the original
> > approach was the risk of calling continue/break_if_contended() in the
> > wrong place, and also the fact you can't really externalize things to
> > a function if you're looking for a cleaner split. At least with
> > drm_exec_until_all_locked() you can do both.
>
> Yeah, but that means that you can't use return inside your code block
> and instead has to define an error label for handling "normal"
> contention which is what I'm trying to avoid here.
>
> How about:
>
> #define drm_exec_until_all_locked(exec) \
> __drm_exec_retry: if (drm_exec_cleanup(exec))
>
>
> #define drm_exec_retry_on_contention(exec) \
> if (unlikely(drm_exec_is_contended(exec))) \
> goto __drm_exec_retry
>
>
> And then use it like:
>
> drm_exec_until_all_locked(exec)
> {
> ret = drm_exec_prepare_obj(exec, obj);
> drm_exec_retry_on_contention(exec);
> }
That would work, and I was about to suggest extending my proposal with
a drm_exec_retry_on_contention() to support both use cases. The only
downside is the fact you might be able to break out of a loop that has
local variables, which will leak stack space.
>
> The only problem I can see with this is that the __drm_exec_retry label
> would be function local.
You can use local labels [1] to make it local to a block (see my
version, just need to rename the retry label into __drm_exec_retry). I
checked, and this is used elsewhere in the kernel (like in
linux/wait.h, which is a core feature), so it should be safe to use.
[1]https://gcc.gnu.org/onlinedocs/gcc/Local-Labels.html
