linux-kernel - Re: [PATCH v2 2/6] bitmap: replace _reg_op(REG_OP_ALLOC) with bitmap

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Message-ID: <ZNl30xC1VFPWl9Ml@yury-ThinkPad>
Date:   Sun, 13 Aug 2023 17:39:47 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v2 2/6] bitmap: replace _reg_op(REG_OP_ALLOC) with
 bitmap_set()

On Fri, Aug 11, 2023 at 03:31:01PM +0200, Rasmus Villemoes wrote:
> On 11/08/2023 14.56, Yury Norov wrote:
> > On Fri, Aug 11, 2023 at 08:21:33AM +0200, Rasmus Villemoes wrote:
> >> On 11/08/2023 02.57, Yury Norov wrote:
> >>> _reg_op(REG_OP_ALLOC) duplicates bitmap_set(). Fix it.
> >>>
> >>> Signed-off-by: Yury Norov <yury.norov@...il.com>
> >>> ---
> >>>  lib/bitmap.c | 5 ++++-
> >>>  1 file changed, 4 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/lib/bitmap.c b/lib/bitmap.c
> >>> index 3a589016f5e0..c9afe704fe4b 100644
> >>> --- a/lib/bitmap.c
> >>> +++ b/lib/bitmap.c
> >>> @@ -1352,9 +1352,12 @@ EXPORT_SYMBOL(bitmap_release_region);
> >>>   */
> >>>  int bitmap_allocate_region(unsigned long *bitmap, unsigned int pos, int order)
> >>>  {
> >>> +	unsigned int nbits = pos + BIT(order);
> >>> +
> >>
> >> That really doesn't sound right. Have you added self-tests for these
> >> functions first and then used those to catch regressions?
> > 
> > When bitmap_allocate_region() is broken, almost every arch build fails
> > to boot. Can you explain what exactly looks wrong to you?
> 
> The number of bits we are about to set should not be [position in bitmap
> to start from] + [2^order]. The second half of that patch was
> 
> -	return __reg_op(bitmap, pos, order, REG_OP_ALLOC);
> +	bitmap_set(bitmap, pos, nbits);
> +	return 0;
> 
> so instead of setting 1<<nbits starting at pos, you're now setting
> pos+(1<<nbits) starting at pos. How is that correct?

You're right. Bad on me. :/

I'll send v3 with all the discussed cleared shortly.

Thanks,
YUry