Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <d81ee557-74b1-6ed9-e806-d8e0865e40f0@rasmusvillemoes.dk>
Date:   Fri, 11 Aug 2023 15:31:01 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.13.0
Subject: Re: [PATCH v2 2/6] bitmap: replace _reg_op(REG_OP_ALLOC) with
 bitmap_set()
Content-Language: en-US, da
To:     Yury Norov <yury.norov@gmail.com>
Cc:     linux-kernel@vger.kernel.org,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>
References: <20230811005732.107718-1-yury.norov@gmail.com>
 <20230811005732.107718-3-yury.norov@gmail.com>
 <25deb65e-a8f3-957b-9e4f-759604111d50@rasmusvillemoes.dk>
 <ZNYv4pt4HBUBZA60@yury-ThinkPad>
From:   Rasmus Villemoes <linux@rasmusvillemoes.dk>
In-Reply-To: <ZNYv4pt4HBUBZA60@yury-ThinkPad>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

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@gmail.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?

Rasmus