linux-kernel - Re: [PATCH 03/11] lightnvm: pblk: check read lba on gc path

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Date:   Wed, 18 Apr 2018 04:53:06 -0700
From:   Javier González <javier@...igon.com>
To:     Matias Bjørling <mb@...htnvm.io>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/11] lightnvm: pblk: check read lba on gc path

> On 17 Apr 2018, at 05.03, Matias Bjørling <mb@...htnvm.io> wrote:
> 
> On 4/16/18 12:25 PM, Javier González wrote:
>> Check that the lba stored in the LBA metadata is correct in the GC path
>> too. This requires a new helper function to check random reads in the
>> vector read.
>> Signed-off-by: Javier González <javier@...xlabs.com>
>> ---
>>  drivers/lightnvm/pblk-read.c | 39 +++++++++++++++++++++++++++++++++------
>>  1 file changed, 33 insertions(+), 6 deletions(-)
>> diff --git a/drivers/lightnvm/pblk-read.c b/drivers/lightnvm/pblk-read.c
>> index 9eee10f69df0..0d45d4ffc370 100644
>> --- a/drivers/lightnvm/pblk-read.c
>> +++ b/drivers/lightnvm/pblk-read.c
>> @@ -113,15 +113,14 @@ static int pblk_submit_read_io(struct pblk *pblk, struct nvm_rq *rqd)
>>  	return NVM_IO_OK;
>>  }
>>  -static void pblk_read_check(struct pblk *pblk, struct nvm_rq *rqd,
>> -			   sector_t blba)
>> +static void pblk_read_check_seq(struct pblk *pblk, void *meta_list,
>> +				sector_t blba, int nr_lbas)
>>  {
>> -	struct pblk_sec_meta *meta_list = rqd->meta_list;
>> -	int nr_lbas = rqd->nr_ppas;
>> +	struct pblk_sec_meta *meta_lba_list = meta_list;
>>  	int i;
>>    	for (i = 0; i < nr_lbas; i++) {
>> -		u64 lba = le64_to_cpu(meta_list[i].lba);
>> +		u64 lba = le64_to_cpu(meta_lba_list[i].lba);
>>    		if (lba == ADDR_EMPTY)
>>  			continue;
>> @@ -130,6 +129,32 @@ static void pblk_read_check(struct pblk *pblk, struct nvm_rq *rqd,
>>  	}
>>  }
>>  +/*
>> + * There can be wholes in the lba list.
>> + */
> 
> holes

Can you change it?

> 
>> +static void pblk_read_check_rand(struct pblk *pblk, void *meta_list,
>> +				u64 *lba_list, int nr_lbas)
>> +{
>> +	struct pblk_sec_meta *meta_lba_list = meta_list;
>> +	int i, j;
>> +
>> +	for (i = 0, j = 0; i < nr_lbas; i++) {
>> +		u64 lba = lba_list[i];
>> +		u64 meta_lba;
>> +
>> +		if (lba == ADDR_EMPTY)
>> +			continue;
>> +
>> +		meta_lba = le64_to_cpu(meta_lba_list[j++].lba);
> 
> You can move the j++ into the for loop. Although, why not use just the i iterator?

Look above, we only increase on valid lbas.

> 
>> +
>> +		if (lba != meta_lba) {
>> +			pr_err("pblk: corrupted read LBA (%llu/%llu)\n",
>> +								lba, meta_lba);
>> +			WARN_ON(1);
> 
> I don't understand this, if a corrupted LBA is found here, how is it
> communicated back to pblk and the LBA can be recovered from elsewhere.
> If the data is wrong, this should have been communicated by the drive
> on the completion path. The drive is defect if this happens.
> 

This happens if a read does not match the lba stored on the LBA. This is
definitely an error and it has helped us in the past to find race
conditions on pblk's read path, specially when forming partial I/Os.

If the read failed from the drive (e.g., when enabling HECC), we still
want information about where it failed for debugging purposes. Same we
do on the normal read path.

Javier

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