Re: [akpm-mm:mm-unstable 75/80] drivers/video/fbdev/core/fb_defio.c:272:3: error: call to undeclared function 'mapping_wrprotect_page'; ISO C99 and later do not support implicit function declarations

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Mon, Feb 03, 2025 at 03:35:48AM +0800, kernel test robot wrote:
> Hi Lorenzo,
>
> FYI, the error/warning was bisected to this commit, please ignore it if it's irrelevant.
>
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-unstable
> head:   7de6fd8ab65003f050aa58e705592745717ed318
> commit: 6a9318f28d7e371692838677c364145fe04b1093 [75/80] fb_defio: do not use deprecated page->mapping, index fields
> config: arm-randconfig-001-20250203 (https://download.01.org/0day-ci/archive/20250203/202502030356.JNL7I49s-lkp@intel.com/config)
> compiler: clang version 18.1.8 (https://github.com/llvm/llvm-project 3b5b5c1ec4a3095ab096dd780e84d7ab81f3d7ff)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250203/202502030356.JNL7I49s-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202502030356.JNL7I49s-lkp@intel.com/
>
> All errors (new ones prefixed by >>):
>
> >> drivers/video/fbdev/core/fb_defio.c:272:3: error: call to undeclared function 'mapping_wrprotect_page'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>      272 |                 mapping_wrprotect_page(fbdefio->mapping, pgoff, 1, page);
>          |                 ^
>    1 error generated.

Hi, thanks for the report.

It's a duplicate of the previous one, as the build bots don't seem to have
any ability to de-dupe reports (not sure if entirely feasible either).

It's because defio, a mechanism that explicitly requires an mmu, doesn't
explicitly express a dependency on CONFIG_MMU, which causes randconfig to
generate totally invalid configurations.

I sent a fix-patch to correct this by adding a Kconfig depends on entry, so
this is addressed.

>
>
> vim +/mapping_wrprotect_page +272 drivers/video/fbdev/core/fb_defio.c
>
>    258
>    259	/* workqueue callback */
>    260	static void fb_deferred_io_work(struct work_struct *work)
>    261	{
>    262		struct fb_info *info = container_of(work, struct fb_info, deferred_work.work);
>    263		struct fb_deferred_io_pageref *pageref, *next;
>    264		struct fb_deferred_io *fbdefio = info->fbdefio;
>    265
>    266		/* here we wrprotect the page's mappings, then do all deferred IO. */
>    267		mutex_lock(&fbdefio->lock);
>    268		list_for_each_entry(pageref, &fbdefio->pagereflist, list) {
>    269			struct page *page = pageref->page;
>    270			pgoff_t pgoff = pageref->offset >> PAGE_SHIFT;
>    271
>  > 272			mapping_wrprotect_page(fbdefio->mapping, pgoff, 1, page);
>    273		}
>    274
>    275		/* driver's callback with pagereflist */
>    276		fbdefio->deferred_io(info, &fbdefio->pagereflist);
>    277
>    278		/* clear the list */
>    279		list_for_each_entry_safe(pageref, next, &fbdefio->pagereflist, list)
>    280			fb_deferred_io_pageref_put(pageref, info);
>    281
>    282		mutex_unlock(&fbdefio->lock);
>    283	}
>    284
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki