Re: [PATCH] powerpc/mm: fix always true/false warning in slice.c

[Mathieu Malaterre]

On Fri, Jun 22, 2018 at 3:49 PM Christophe Leroy
<christophe.leroy@xxxxxx> wrote:
>
> This patch fixes the following warnings (obtained with make W=1).
>
> arch/powerpc/mm/slice.c: In function 'slice_range_to_mask':
> arch/powerpc/mm/slice.c:73:12: error: comparison is always true due to limited range of data type [-Werror=type-limits]
>   if (start < SLICE_LOW_TOP) {
>             ^
> arch/powerpc/mm/slice.c:81:20: error: comparison is always false due to limited range of data type [-Werror=type-limits]
>   if ((start + len) > SLICE_LOW_TOP) {
>                     ^
> arch/powerpc/mm/slice.c: In function 'slice_mask_for_free':
> arch/powerpc/mm/slice.c:136:17: error: comparison is always true due to limited range of data type [-Werror=type-limits]
>   if (high_limit <= SLICE_LOW_TOP)
>                  ^
> arch/powerpc/mm/slice.c: In function 'slice_check_range_fits':
> arch/powerpc/mm/slice.c:185:12: error: comparison is always true due to limited range of data type [-Werror=type-limits]
>   if (start < SLICE_LOW_TOP) {
>             ^
> arch/powerpc/mm/slice.c:195:39: error: comparison is always false due to limited range of data type [-Werror=type-limits]
>   if (SLICE_NUM_HIGH && ((start + len) > SLICE_LOW_TOP)) {
>                                        ^
> arch/powerpc/mm/slice.c: In function 'slice_scan_available':
> arch/powerpc/mm/slice.c:306:11: error: comparison is always true due to limited range of data type [-Werror=type-limits]
>   if (addr < SLICE_LOW_TOP) {
>            ^
> arch/powerpc/mm/slice.c: In function 'get_slice_psize':
> arch/powerpc/mm/slice.c:709:11: error: comparison is always true due to limited range of data type [-Werror=type-limits]
>   if (addr < SLICE_LOW_TOP) {
>            ^
>
> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
> ---
>  arch/powerpc/mm/slice.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
> index 9530c6db406a..17c57760e06c 100644
> --- a/arch/powerpc/mm/slice.c
> +++ b/arch/powerpc/mm/slice.c
> @@ -62,6 +62,13 @@ static void slice_print_mask(const char *label, const struct slice_mask *mask) {
>
>  #endif
>
> +static inline bool slice_addr_is_low(unsigned long addr)
> +{
> +       u64 tmp = (u64)addr;
> +
> +       return tmp < SLICE_LOW_TOP;
> +}
> +
>  static void slice_range_to_mask(unsigned long start, unsigned long len,
>                                 struct slice_mask *ret)
>  {
> @@ -71,7 +78,7 @@ static void slice_range_to_mask(unsigned long start, unsigned long len,
>         if (SLICE_NUM_HIGH)
>                 bitmap_zero(ret->high_slices, SLICE_NUM_HIGH);
>
> -       if (start < SLICE_LOW_TOP) {
> +       if (slice_addr_is_low(start)) {
>                 unsigned long mend = min(end,
>                                          (unsigned long)(SLICE_LOW_TOP - 1));
>
> @@ -79,7 +86,7 @@ static void slice_range_to_mask(unsigned long start, unsigned long len,
>                         - (1u << GET_LOW_SLICE_INDEX(start));
>         }
>
> -       if ((start + len) > SLICE_LOW_TOP) {
> +       if (!slice_addr_is_low(end)) {
>                 unsigned long start_index = GET_HIGH_SLICE_INDEX(start);
>                 unsigned long align_end = ALIGN(end, (1UL << SLICE_HIGH_SHIFT));
>                 unsigned long count = GET_HIGH_SLICE_INDEX(align_end) - start_index;
> @@ -134,7 +141,7 @@ static void slice_mask_for_free(struct mm_struct *mm, struct slice_mask *ret,
>                 if (!slice_low_has_vma(mm, i))
>                         ret->low_slices |= 1u << i;
>
> -       if (high_limit <= SLICE_LOW_TOP)
> +       if (slice_addr_is_low(high_limit - 1))

Is high_limit ever going to be 0 ?

>                 return;
>
>         for (i = 0; i < GET_HIGH_SLICE_INDEX(high_limit); i++)
> @@ -183,7 +190,7 @@ static bool slice_check_range_fits(struct mm_struct *mm,
>         unsigned long end = start + len - 1;
>         u64 low_slices = 0;
>
> -       if (start < SLICE_LOW_TOP) {
> +       if (slice_addr_is_low(start)) {
>                 unsigned long mend = min(end,
>                                          (unsigned long)(SLICE_LOW_TOP - 1));
>
> @@ -193,7 +200,7 @@ static bool slice_check_range_fits(struct mm_struct *mm,
>         if ((low_slices & available->low_slices) != low_slices)
>                 return false;
>
> -       if (SLICE_NUM_HIGH && ((start + len) > SLICE_LOW_TOP)) {
> +       if (SLICE_NUM_HIGH && !slice_addr_is_low(end)) {
>                 unsigned long start_index = GET_HIGH_SLICE_INDEX(start);
>                 unsigned long align_end = ALIGN(end, (1UL << SLICE_HIGH_SHIFT));
>                 unsigned long count = GET_HIGH_SLICE_INDEX(align_end) - start_index;
> @@ -304,7 +311,7 @@ static bool slice_scan_available(unsigned long addr,
>                                  int end, unsigned long *boundary_addr)
>  {
>         unsigned long slice;
> -       if (addr < SLICE_LOW_TOP) {
> +       if (slice_addr_is_low(addr)) {
>                 slice = GET_LOW_SLICE_INDEX(addr);
>                 *boundary_addr = (slice + end) << SLICE_LOW_SHIFT;
>                 return !!(available->low_slices & (1u << slice));
> @@ -707,7 +714,7 @@ unsigned int get_slice_psize(struct mm_struct *mm, unsigned long addr)
>
>         VM_BUG_ON(radix_enabled());
>
> -       if (addr < SLICE_LOW_TOP) {
> +       if (slice_addr_is_low(addr)) {
>                 psizes = mm->context.low_slices_psize;
>                 index = GET_LOW_SLICE_INDEX(addr);
>         } else {
> --
> 2.13.3
>