Re: [PATCH v2 1/2] list: add missing empty list check to list_cut_before()

[Andy Shevchenko]

On Fri, Sep 18, 2026 at 12:14:56AM +0800, Ziran Zhang wrote:
> On Thu, 17 Sep 2026 18:21:45 +0300, Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
> > The kernel-doc specifically says:
> > 
> >   'You should pass in @entry an element you know is on @head.'
> > 
> > Do you have a real life example?
> 
> No, I do not have a real life example.  It was based on code
> analysis only.
> 
> > The room of the lines for the body of the commit message is ~72
> > characters and not 56.
> 
> Noted, I will keep that in mind for future patches.
> 
> > What makes it different to the similar cases in list_splice(), for
> > example?
> 
> list_splice() has an empty-list check too, on its source list:
> 
> 	if (!list_empty(list))
> 		__list_splice(list, head, head->next);
> 
> list_cut_position() does the same for its source list:
> 
> 	if (list_empty(head))
> 		return;
> 
> But list_cut_position() has the same kernel-doc wording:
> 
>   'You should pass on @entry an element you know is on @head.'
> 
> and still returns early for an empty head.
> 
> So list_cut_position() handles an empty head before doing any pointer
> updates, even though the kernel-doc contract only requires @entry to
> be on @head.  My patch makes list_cut_before() do the same.
> 
> I agree this is a defensive change, not a bug fix.  If the consensus
> is to rely strictly on the caller contract, I will drop this series.
> 
> For list_cut_before() specifically, making it match list_cut_position()
> seemed reasonable.

Please, summarize the above and elaborate all this in the commit message
in the next version.

-- 
With Best Regards,
Andy Shevchenko