linux-kernel - Re: [PATCH] lightnvm: pblk: advance bio according to lba index

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Date:   Thu, 27 Jul 2017 18:33:17 +0200
From:   Javier González <jg@...htnvm.io>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Matias Bjørling <mb@...htnvm.io>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lightnvm: pblk: advance bio according to lba index

> On 27 Jul 2017, at 18.31, Jens Axboe <axboe@...nel.dk> wrote:
> 
> On 07/27/2017 08:49 AM, Javier González wrote:
>> When a lba either hits the cache or corresponds to an empty entry in the
>> L2P table, we need to advance the bio according to the position in which
>> the lba is located. Otherwise, we will copy data in the wrong page, thus
>> causing data corruption for the application.
>> 
>> In case of a cache hit, we assumed that bio->bi_iter.bi_idx would
>> contain the correct index, but this is no necessarily true. Instead, use
>> the local bio advance counter and iterator. This guarantees that lbas
>> hitting the cache are copied into the right bv_page.
>> 
>> In case of an empty L2P entry, we omitted to advance the bio. In the
>> cases when the same I/O also contains a cache hit, data corresponding
>> to this lba will be copied to the wrong bv_page. Fix this by advancing
>> the bio as we do in the case of a cache hit.
>> 
>> Fixes: a4bd217b4326 lightnvm: physical block device (pblk) target
>> 
>> Signed-off-by: Javier González <javier@...igon.com>
>> ---
>> drivers/lightnvm/pblk-rb.c   |  4 ++--
>> drivers/lightnvm/pblk-read.c | 19 ++++++++++++++-----
>> drivers/lightnvm/pblk.h      |  2 +-
>> 3 files changed, 17 insertions(+), 8 deletions(-)
>> 
>> diff --git a/drivers/lightnvm/pblk-rb.c b/drivers/lightnvm/pblk-rb.c
>> index 5ecc154f6831..2e88c3d6d9a1 100644
>> --- a/drivers/lightnvm/pblk-rb.c
>> +++ b/drivers/lightnvm/pblk-rb.c
>> @@ -657,7 +657,7 @@ unsigned int pblk_rb_read_to_bio(struct pblk_rb *rb, struct nvm_rq *rqd,
>>  * be directed to disk.
>>  */
>> int pblk_rb_copy_to_bio(struct pblk_rb *rb, struct bio *bio, sector_t lba,
>> -			struct ppa_addr ppa, int bio_iter)
>> +			struct ppa_addr ppa, int bio_iter, int advanced_bio)
> 
> This would be cleaner as a 'bool advance_bio' as both the type and as a
> reversed info on whether to do the advance or not.

I'll fix it.

Thanks Jens.

Javier

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