linux-kernel - Re: [PATCH v1 1/2] lib/test_bitmap: Correct test data offsets for 32-bit

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Date:   Wed, 8 Jan 2020 22:26:54 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH v1 1/2] lib/test_bitmap: Correct test data offsets for
 32-bit

On Wed, Jan 08, 2020 at 11:24:37AM -0800, Yury Norov wrote:
> On Wed, Jan 08, 2020 at 08:46:10PM +0200, Andy Shevchenko wrote:
> > On 32-bit platform the size of long is only 32 bits which makes wrong offset
> > in the array of 64 bit size.
> > 
> > Calculate offset based on BITS_PER_LONG.
> > 
> > Fixes: 30544ed5de43 ("lib/bitmap: introduce bitmap_replace() helper")
> > Reported-by: Guenter Roeck <linux@...ck-us.net>
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

> >  	unsigned int nbits = 64;
> > +	unsigned int step = DIV_ROUND_UP(nbits, BITS_PER_LONG);
> 
> Step is already defined in this file:
>         #define step (sizeof(u64) / sizeof(unsigned long))

...and later undefined.

> to avoid the same problem in other test cases. Introducing another variant of 
> it looks messy.

I don't see any problem.

> 
> >  	DECLARE_BITMAP(bmap, 1024);
> >  
> >  	bitmap_zero(bmap, 1024);
> > -	bitmap_replace(bmap, &exp2[0], &exp2[1], exp2_to_exp3_mask, nbits);
> > +	bitmap_replace(bmap, &exp2[0 * step], &exp2[1 * step], exp2_to_exp3_mask, nbits);
> >  	expect_eq_bitmap(bmap, exp3_0_1, nbits);
> 
> If nbits is always 64, why don't you pass 64 directly?

We may use any setting. For now it's 64, but nothing prevents us to extend to,
let's say, 75.

-- 
With Best Regards,
Andy Shevchenko