Re: [PATCH 08/13] lightnvm: pblk: Set proper read stutus in bio

Javier González
2019-03-04T13:21:16Z

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> On 4 Mar 2019, at 14.04, Matias Bjørling <mb@lightnvm.io> wrote:
>
> On 3/4/19 10:48 AM, Javier González wrote:
>>> On 4 Mar 2019, at 10.35, Hans Holmberg <hans.ml.holmberg@owltronix.com> wrote:
>>>
>>> On Mon, Mar 4, 2019 at 9:03 AM Javier González <javier@javigon.com> wrote:
>>>>> On 27 Feb 2019, at 18.14, Igor Konopko <igor.j.konopko@intel.com> wrote:
>>>>>
>>>>> Currently in case of read errors, bi_status is not
>>>>> set properly which leads to returning inproper data
>>>>> to higher layer. This patch fix that by setting proper
>>>>> status in case of read errors
>>>>>
>>>>> Patch also removes unnecessary warn_once(), which does
>>>>> not make sense in that place, since user bio is not used
>>>>> for interation with drive and thus bi_status will not be
>>>>> set here.
>>>>>
>>>>> Signed-off-by: Igor Konopko <igor.j.konopko@intel.com>
>>>>> ---
>>>>> drivers/lightnvm/pblk-read.c | 11 +++++------
>>>>> 1 file changed, 5 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/drivers/lightnvm/pblk-read.c b/drivers/lightnvm/pblk-read.c
>>>>> index 3789185144da..39c1d6ccaedb 100644
>>>>> --- a/drivers/lightnvm/pblk-read.c
>>>>> +++ b/drivers/lightnvm/pblk-read.c
>>>>> @@ -175,11 +175,10 @@ static void pblk_read_check_rand(struct pblk *pblk, struct nvm_rq *rqd,
>>>>> WARN_ONCE(j != rqd->nr_ppas, "pblk: corrupted random request\n");
>>>>> }
>>>>>
>>>>> -static void pblk_end_user_read(struct bio *bio)
>>>>> +static void pblk_end_user_read(struct bio *bio, int error)
>>>>> {
>>>>> -#ifdef CONFIG_NVM_PBLK_DEBUG
>>>>> - WARN_ONCE(bio->bi_status, "pblk: corrupted read bio\n");
>>>>> -#endif
>>>>> + if (error && error != NVM_RSP_WARN_HIGHECC)
>>>>> + bio_io_error(bio);
>>>>> bio_endio(bio);
>>>>> }
>>>>>
>>>>> @@ -219,7 +218,7 @@ static void pblk_end_io_read(struct nvm_rq *rqd)
>>>>> struct pblk_g_ctx *r_ctx = nvm_rq_to_pdu(rqd);
>>>>> struct bio *bio = (struct bio *)r_ctx->private;
>>>>>
>>>>> - pblk_end_user_read(bio);
>>>>> + pblk_end_user_read(bio, rqd->error);
>>>>> __pblk_end_io_read(pblk, rqd, true);
>>>>> }
>>>>>
>>>>> @@ -292,7 +291,7 @@ static void pblk_end_partial_read(struct nvm_rq *rqd)
>>>>> rqd->bio = NULL;
>>>>> rqd->nr_ppas = nr_secs;
>>>>>
>>>>> - bio_endio(bio);
>>>>> + pblk_end_user_read(bio, rqd->error);
>>>>> __pblk_end_io_read(pblk, rqd, false);
>>>>> }
>>>>>
>>>>> --
>>>>> 2.17.1
>>>>
>>>> This is by design. We do not report the read errors as in any other
>>>> block device - this is why we clone the read bio.
>>>
>>> Could you elaborate on why not reporting read errors is a good thing in pblk?
>> Normal block devices do not report read errors on the completion path
>> unless it is a fatal error. This is actually not well understood by the
>> upper layers, which tend to assume that the device is completely broken.
>> This is a challenge for OCSSD / Denali / Zone devices as there are cases
>> where reads can fail. Unfortunately at this point, we need to mask these
>> errors and deal with them in the different layers.
>
> Please don't include zone devices in that list. ZAC/ZBC are
> well-behaved, and an error is a real error.

They have worked around this for years. AFAIK the read path still
returns predefined data, not an error. So, as I see it is the same

Javier

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