linux-kernel - Re: [PATCH v2 01/12] md/raid5: Factor out ahead_of

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Date:   Thu, 21 Apr 2022 10:05:19 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
Cc:     linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
        Song Liu <song@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Guoqing Jiang <guoqing.jiang@...ux.dev>,
        Stephen Bates <sbates@...thlin.com>,
        Martin Oliveira <Martin.Oliveira@...eticom.com>,
        David Sloan <David.Sloan@...eticom.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 01/12] md/raid5: Factor out ahead_of_reshape() function



On 2022-04-21 03:17, Paul Menzel wrote:
> Dear Logan,
> 
> 
> Thank you for these patches.
> 
> 
> Am 20.04.22 um 21:54 schrieb Logan Gunthorpe:
>> There are a few uses of an ugly ternary operator in raid5_make_request()
>> to check if a sector is a head of a reshape sector.
>>
>> Factor this out into a simple helper called ahead_of_reshape().
>>
>> This appears to fix the first bio_wouldblock_error() check which appears
>> to have comparison operators that didn't match the check below which
>> causes a schedule. Besides this, no functional changes intended.
> 
> If there is an error, could that be fixed in a separate commit, which
> could be applied to the stable series?

Yes, sure. Though, I'm not 100% sure there's an error or noticeable bug.
It's just that the logic didn't match and it made cleaning up the code
overly complicated.


> 
>> Suggested-by: Christoph Hellwig <hch@....de>
>> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
>> ---
>>   drivers/md/raid5.c | 29 +++++++++++++++++------------
>>   1 file changed, 17 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
>> index 7f7d1546b9ba..97b23c18402b 100644
>> --- a/drivers/md/raid5.c
>> +++ b/drivers/md/raid5.c
>> @@ -5787,6 +5787,15 @@ static void make_discard_request(struct mddev
>> *mddev, struct bio *bi)
>>       bio_endio(bi);
>>   }
>>   +static bool ahead_of_reshape(struct mddev *mddev, sector_t sector,
>> +                 sector_t reshape_sector)
>> +{
>> +    if (mddev->reshape_backwards)
>> +        return sector < reshape_sector;
>> +    else
>> +        return sector >= reshape_sector;
> 
> I like the ternary operator. ;-)
> 
>     return mddev->reshape_backwards ? (return sector < reshape_sector) :
> (sector >= reshape_sector)
> 
> Sorry, does not matter.

Yeah, I think plenty of people do not, though; it's harder to read with
the long line and awkward to wrap.

> Reviewed-by: Paul Menzel <pmenzel@...gen.mpg.de>

Thanks,

Logan