Re: [PATCH 2/2] x86: make __get_wchan() use arch_stack_walk()

[Qi Zheng]

On 2023/4/12 13:20, Josh Poimboeuf wrote:
> On Sun, Apr 09, 2023 at 02:30:23PM +0800, Qi Zheng wrote:
> > On 2023/4/9 06:12, Josh Poimboeuf wrote:
> > > On Sat, Apr 08, 2023 at 01:36:06PM +0800, Qi Zheng wrote:
> > > > On 2023/4/8 13:08, Josh Poimboeuf wrote:
> > > > > On Thu, Mar 30, 2023 at 04:15:52PM +0800, Qi Zheng wrote:
> > > > > > Make __get_wchan() use arch_stack_walk() directly to
> > > > > > avoid open-coding of unwind logic.
> > > > > >
> > > > > > Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> > > > >
> > > > > Can we just have a shared version of __get_wchan() for all
> > > > > CONFIG_ARCH_STACKWALK arches?
> > > >
> > > >   From a quick glance, I think it's ok, but we still need to define
> > > > the arch's own get_wchan_cb(). I will try to do it.
> > >
> > > Hm, why would we need to do that?
> >
> > Because I see checks for count++ < 16 exist in __get_wchan() for some
> > arches and some don't. So I'm not sure if this check can be discarded
> > after using arch_stack_walk(). And I see that this check is retained in
> > arm64, see [1] for details.
> >
> > [1]. https://github.com/torvalds/linux/commit/4f62bb7cb165f3e7b0a91279fe9dd5c56daf3457
>
> That difference seems to have nothing to do with individual arch
> differences.
>
> The 16-check limit looks like some ancient cargo cult ritual which was
> copy-pasted decades ago, presumably to avoid some kind of infinite stack
> recursion loop in scheduler code, which should never happen.  That
> should definitely be removed.

Got it.

> Another good reason to unify them, to get rid of cruft like that.

OK, will try to make a shared version of __get_wchan() for all
CONFIG_ARCH_STACKWALK arches.

Thanks,
Qi

>