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

[Christophe LEROY]

Le 22/06/2018 Ã 16:55, Mathieu Malaterre a ÃcritÂ:
> 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 ?

See slice_get_unmapped_area(), high_limit will never be 0.

Christophe

> >                  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