Re: [PATCH] scsi: target: tcmu: Call flush_dcache_page() with proper page struct

[Henry Willard <henry.willard@oracle.com>]

On 6/19/20 6:31 PM, kernel test robot wrote:
> Hi Henry,
>
> Thank you for the patch! Perhaps something to improve:
>
> [auto build test WARNING on mkp-scsi/for-next]
> [also build test WARNING on scsi/for-next v5.8-rc1 next-20200618]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use  as documented in
> https://git-scm.com/docs/git-format-patch]
>
> url:    https://github.com/0day-ci/linux/commits/Henry-Willard/scsi-target-tcmu-Call-flush_dcache_page-with-proper-page-struct/20200620-024740
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/mkp/scsi.git for-next
> config: xtensa-allyesconfig (attached as .config)
> compiler: xtensa-linux-gcc (GCC) 9.3.0
> reproduce (this is a W=1 build):
>          wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>          chmod +x ~/bin/make.cross
>          # save the attached .config to linux build tree
>          COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=xtensa
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
>
> All warnings (new ones prefixed by >>, old ones prefixed by <<):
>
> In file included from include/linux/kernel.h:11,
> from include/linux/list.h:9,
> from include/linux/preempt.h:11,
> from include/linux/spinlock.h:51,
> from drivers/target/target_core_user.c:9:
> include/linux/scatterlist.h: In function 'sg_set_buf':
> arch/xtensa/include/asm/page.h:193:9: warning: comparison of unsigned expression >= 0 is always true [-Wtype-limits]
> 193 |  ((pfn) >= ARCH_PFN_OFFSET && ((pfn) - ARCH_PFN_OFFSET) < max_mapnr)
> |         ^~
> include/linux/compiler.h:78:42: note: in definition of macro 'unlikely'
> 78 | # define unlikely(x) __builtin_expect(!!(x), 0)
> |                                          ^
> include/linux/scatterlist.h:143:2: note: in expansion of macro 'BUG_ON'
> 143 |  BUG_ON(!virt_addr_valid(buf));
> |  ^~~~~~
> arch/xtensa/include/asm/page.h:201:32: note: in expansion of macro 'pfn_valid'
> 201 | #define virt_addr_valid(kaddr) pfn_valid(__pa(kaddr) >> PAGE_SHIFT)
> |                                ^~~~~~~~~
> include/linux/scatterlist.h:143:10: note: in expansion of macro 'virt_addr_valid'
> 143 |  BUG_ON(!virt_addr_valid(buf));
> |          ^~~~~~~~~~~~~~~
> In file included from ./arch/xtensa/include/generated/asm/bug.h:1,
> from include/linux/bug.h:5,
> from include/linux/thread_info.h:12,
> from include/asm-generic/preempt.h:5,
> from ./arch/xtensa/include/generated/asm/preempt.h:1,
> from include/linux/preempt.h:78,
> from include/linux/spinlock.h:51,
> from drivers/target/target_core_user.c:9:
> include/linux/dma-mapping.h: In function 'dma_map_resource':
> arch/xtensa/include/asm/page.h:193:9: warning: comparison of unsigned expression >= 0 is always true [-Wtype-limits]
> 193 |  ((pfn) >= ARCH_PFN_OFFSET && ((pfn) - ARCH_PFN_OFFSET) < max_mapnr)
> |         ^~
> include/asm-generic/bug.h:144:27: note: in definition of macro 'WARN_ON_ONCE'
> 144 |  int __ret_warn_once = !!(condition);            |                           ^~~~~~~~~
> include/linux/dma-mapping.h:352:19: note: in expansion of macro 'pfn_valid'
> 352 |  if (WARN_ON_ONCE(pfn_valid(PHYS_PFN(phys_addr))))
> |                   ^~~~~~~~~
> In file included from include/linux/mm_types_task.h:16,
> from include/linux/mm_types.h:5,
> from include/linux/mmzone.h:21,
> from include/linux/gfp.h:6,
> from include/linux/umh.h:4,
> from include/linux/kmod.h:9,
> from include/linux/module.h:16,
> from drivers/target/target_core_user.c:10:
> drivers/target/target_core_user.c: In function 'tcmu_flush_dcache_range':
> arch/xtensa/include/asm/page.h:193:9: warning: comparison of unsigned expression >= 0 is always true [-Wtype-limits]
> 193 |  ((pfn) >= ARCH_PFN_OFFSET && ((pfn) - ARCH_PFN_OFFSET) < max_mapnr)
> |         ^~
> arch/xtensa/include/asm/page.h:201:32: note: in expansion of macro 'pfn_valid'
> 201 | #define virt_addr_valid(kaddr) pfn_valid(__pa(kaddr) >> PAGE_SHIFT)
> |                                ^~~~~~~~~
> drivers/target/target_core_user.c:605:7: note: in expansion of macro 'virt_addr_valid'
> 605 |   if (virt_addr_valid(start))
> |       ^~~~~~~~~~~~~~~
>>> drivers/target/target_core_user.c:600:15: warning: variable 'pg' set but not used [-Wunused-but-set-variable]
> 600 |  struct page *pg;
> |               ^~
>
> vim +/pg +600 drivers/target/target_core_user.c
>
>     595	
>     596	static inline void tcmu_flush_dcache_range(void *vaddr, size_t size)
>     597	{
>     598		unsigned long offset = offset_in_page(vaddr);
>     599		void *start = vaddr - offset;
>   > 600		struct page *pg;
>     601	
>     602		size = round_up(size+offset, PAGE_SIZE);
>     603	
>     604		while (size) {
>     605			if (virt_addr_valid(start))
>     606				pg = virt_to_page(start);
>     607			else if (is_vmalloc_addr(start))
>     608				pg = vmalloc_to_page(start);
>     609			else
>     610				break;
>     611	
>     612			flush_dcache_page(pg);
>     613			start += PAGE_SIZE;
>     614			size -= PAGE_SIZE;
>     615		}
>     616	}
>     617	
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
It doesn't really matter in this case because this patch has been 
superseded by a different fix, but the warning appears to be caused by 
an incorrect implementation of flush_dcache_page() in 
arch/xtensa/include/asm/cacheflush.h. Depending on the variant and 
options, flush_dcache_page can be defined as "do { } while (0)", which 
covers the default null implementation of flush_dcache_page().

Thanks,
Henry