linux-kernel - Re: [PATCH 1/4] bitmap: Modify bitmap_set

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Message-ID: <CACG_h5qjvPN-LFH-JGm=8xeM-k4KB9pd==xvf0DDBMgRb-TXUQ@mail.gmail.com>
Date:   Fri, 20 Nov 2020 23:32:53 +0530
From:   Syed Nayyar Waris <syednwaris@...il.com>
To:     William Breathitt Gray <vilhelm.gray@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] bitmap: Modify bitmap_set_value() to check bitmap length

On Fri, Nov 20, 2020 at 11:29 PM William Breathitt Gray
<vilhelm.gray@...il.com> wrote:
>
> On Fri, Nov 20, 2020 at 11:14:16PM +0530, Syed Nayyar Waris wrote:
> > Add explicit check to see if the value being written into the bitmap
> > does not fall outside the bitmap.
> > The situation that it is falling outside would never be possible in the
> > code because the boundaries are required to be correct before the function
> > is called. The responsibility is on the caller for ensuring the boundaries
> > are correct.
> > This is just to suppress the GCC -Wtype-limits warnings.
>
> Hi Syed,
>
> This commit message sounds a bit strange without the context of our
> earlier discussion thread. Would you be able to reword the commit
> message to explain the motivation for using __builtin_unreachable()?
>
> Thanks,
>
> William Breathitt Gray

Hi William,

Actually I explained the motivation for using __builtin_unreachable()
in the cover letter.
So, left it here in this patch.

I am sending this patch again updating the commit message.

Regards
Syed Nayyar Waris

>
> >
> > Cc: Arnd Bergmann <arnd@...db.de>
> > Signed-off-by: Syed Nayyar Waris <syednwaris@...il.com>
> > Acked-by: William Breathitt Gray <vilhelm.gray@...il.com>
> > ---
> >  include/linux/bitmap.h | 35 +++++++++++++++++++++--------------
> >  1 file changed, 21 insertions(+), 14 deletions(-)
> >
> > diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
> > index 386d08777342..efb6199ea1e7 100644
> > --- a/include/linux/bitmap.h
> > +++ b/include/linux/bitmap.h
> > @@ -78,8 +78,9 @@
> >   *  bitmap_get_value(map, start, nbits)              Get bit value of size
> >   *                                              'nbits' from map at start
> >   *  bitmap_set_value8(map, value, start)        Set 8bit value to map at start
> > - *  bitmap_set_value(map, value, start, nbits)       Set bit value of size 'nbits'
> > - *                                              of map at start
> > + *  bitmap_set_value(map, nbits, value, value_width, start)
> > + *                                              Set bit value of size value_width
> > + *                                              to map at start
> >   *
> >   * Note, bitmap_zero() and bitmap_fill() operate over the region of
> >   * unsigned longs, that is, bits behind bitmap till the unsigned long
> > @@ -610,30 +611,36 @@ static inline void bitmap_set_value8(unsigned long *map, unsigned long value,
> >  }
> >
> >  /**
> > - * bitmap_set_value - set n-bit value within a memory region
> > + * bitmap_set_value - set value within a memory region
> >   * @map: address to the bitmap memory region
> > - * @value: value of nbits
> > - * @start: bit offset of the n-bit value
> > - * @nbits: size of value in bits (must be between 1 and BITS_PER_LONG inclusive).
> > + * @nbits: size of map in bits
> > + * @value: value of clump
> > + * @value_width: size of value in bits (must be between 1 and BITS_PER_LONG inclusive)
> > + * @start: bit offset of the value
> >   */
> > -static inline void bitmap_set_value(unsigned long *map,
> > -                                 unsigned long value,
> > -                                 unsigned long start, unsigned long nbits)
> > +static inline void bitmap_set_value(unsigned long *map, unsigned long nbits,
> > +                                 unsigned long value, unsigned long value_width,
> > +                                 unsigned long start)
> >  {
> > -     const size_t index = BIT_WORD(start);
> > +     const unsigned long index = BIT_WORD(start);
> > +     const unsigned long length = BIT_WORD(nbits);
> >       const unsigned long offset = start % BITS_PER_LONG;
> >       const unsigned long ceiling = round_up(start + 1, BITS_PER_LONG);
> >       const unsigned long space = ceiling - start;
> >
> > -     value &= GENMASK(nbits - 1, 0);
> > +     value &= GENMASK(value_width - 1, 0);
> >
> > -     if (space >= nbits) {
> > -             map[index] &= ~(GENMASK(nbits - 1, 0) << offset);
> > +     if (space >= value_width) {
> > +             map[index] &= ~(GENMASK(value_width - 1, 0) << offset);
> >               map[index] |= value << offset;
> >       } else {
> >               map[index + 0] &= ~BITMAP_FIRST_WORD_MASK(start);
> >               map[index + 0] |= value << offset;
> > -             map[index + 1] &= ~BITMAP_LAST_WORD_MASK(start + nbits);
> > +
> > +             if (index + 1 >= length)
> > +                     __builtin_unreachable();
> > +
> > +             map[index + 1] &= ~BITMAP_LAST_WORD_MASK(start + value_width);
> >               map[index + 1] |= value >> space;
> >       }
> >  }
> > --
> > 2.29.0
> >