linux-kernel - Re: [PATCH 1/2] IB/hfi1: Fix a parameter of find_first

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Date:   Sat, 27 Aug 2016 07:25:02 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     linux-kernel@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 1/2] IB/hfi1: Fix a parameter of find_first_bit.

Le 26/08/2016 à 15:35, Doug Ledford a écrit :
> On 8/26/2016 12:49 AM, Christophe JAILLET wrote:
>> The 2nd parameter of 'find_first_bit' is the number of bits to search.
>> In this case, we are passing 'sizeof(unsigned long)' which is likely to
>> be 4 or 8.
> If the size can be 4 or 8, then using 64 universally is not correct.
> Why not use sizeof() * 8 (or << 3)?
I agree with you...

BTW, the log message is wrong. 'port_mask' is a u64. (not an unsigned 
long). So the sizeof should always be 8.
(cut and paste error from another patch, sorry)

>
>> It is likely that the number of bits of 'port_mask' was expected 
>> here. This
>> variable is a 'u64', so use 64 instead.
>>
>> It has been spotted by the following coccinelle script:
>> @@
>> expression ret, x;
>>
>> @@
>> *  ret = \(find_first_bit \| find_first_zero_bit\) (x, sizeof(...));
>>
>> Signed-off-by: Christophe JAILLET 
>> <christophe.jaillet@...adoo.fr>
>> ---
>> Not sure that using 64 directly is the best option.
>> Maybe '8 * sizeof(port_mask)' as used in the same file for
>> 'for_each_set_bit' would be better
>> ---
... as noted here

Would you like a v2 patch or, will you update it by yourself?

Best regards,
CJ

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