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

["Matias Bjørling" <mb@lightnvm.io>]

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.

> 
> For OCSSD currently, we do this in pblk, which I think fits well the
> model as we exposed a normal block device.
> 
> Javier
>