[PATCH 01/15] mm: various small mmap_prepare cleanups

[Lorenzo Stoakes (Oracle)]

On Thu, Mar 12, 2026 at 02:14:25PM -0700, Andrew Morton wrote:
> On Thu, 12 Mar 2026 20:27:16 +0000 "Lorenzo Stoakes (Oracle)" <ljs at kernel.org> wrote:
>
> > +int mmap_action_prepare(struct vm_area_desc *desc,
> > +			struct mmap_action *action)
> > +
> >  {
> >  	switch (action->type) {
> >  	case MMAP_NOTHING:
> > -		break;
> > +		return 0;
> >  	case MMAP_REMAP_PFN:
> > -		remap_pfn_range_prepare(desc, action->remap.start_pfn);
> > -		break;
> > +		return remap_pfn_range_prepare(desc, action);
> >  	case MMAP_IO_REMAP_PFN:
> > -		io_remap_pfn_range_prepare(desc, action->remap.start_pfn,
> > -					   action->remap.size);
> > -		break;
> > +		return io_remap_pfn_range_prepare(desc, action);
> >  	}
> >  }
> >  EXPORT_SYMBOL(mmap_action_prepare);
>
> hm, was this the correct version?
>
> mm/util.c: In function 'mmap_action_prepare':
> mm/util.c:1451:1: error: control reaches end of non-void function [-Werror=return-type]
>  1451 | }

Seems different compiler versions do different things :)

In theory we should never hit that but memory corruption and err... rogue
drivers? could cause it ofc :)

Will fix on respin.

>
> --- a/mm/util.c~mm-various-small-mmap_prepare-cleanups-fix
> +++ a/mm/util.c
> @@ -1356,6 +1356,8 @@ int mmap_action_prepare(struct vm_area_d
>  		return remap_pfn_range_prepare(desc, action);
>  	case MMAP_IO_REMAP_PFN:
>  		return io_remap_pfn_range_prepare(desc, action);
> +	default:
> +		BUG();

I'd probably prefer a WARN_ON_ONCE(1) return -EBLAH; will think about it on
respin.

>  	}
>  }
>  EXPORT_SYMBOL(mmap_action_prepare);
> _
>

Cheers, Lorenzo