Re: [PATCH v1 11/11] mtd: new support oops logger based on pstore/blk

Miquel Raynal
2020-02-06T15:46:30Z

Hi liao,

liaoweixiong <liaoweixiong@allwinnertech.com> wrote on Thu, 6 Feb 2020
21:10:47 +0800:

> hi Miquel Raynal,
>
> On 2020/1/23 AM 1:41, Miquel Raynal wrote:
> > Hello,
> >
> >
> >>>>>> +/*
> >>>>>> + * All zones will be read as pstore/blk will read zone one by one when do
> >>>>>> + * recover.
> >>>>>> + */
> >>>>>> +static ssize_t mtdpstore_read(char *buf, size_t size, loff_t off)
> >>>>>> +{
> >>>>>> + struct mtdpstore_context *cxt = &oops_cxt;
> >>>>>> + size_t retlen;
> >>>>>> + int ret;
> >>>>>> +
> >>>>>> + if (mtdpstore_block_isbad(cxt, off))
> >>>>>> + return -ENEXT;
> >>>>>> +
> >>>>>> + pr_debug("try to read off 0x%llx size %zu\n", off, size);
> >>>>>> + ret = mtd_read(cxt->mtd, off, size, &retlen, (u_char *)buf);
> >>>>>> + if ((ret < 0 && !mtd_is_bitflip(ret)) || size != retlen) {
> >>>>>
> >>>>> IIRC size != retlen does not mean it failed, but that you should
> >>>>> continue reading after retlen bytes, no?
> >>>>> >>
> >>>> Yes, you are right. I will fix it. Thanks.
> >>>> >>>>> Also, mtd_is_bitflip() does not mean that you are reading a false
> >>>>> buffer, but that the data has been corrected as it contained bitflips.
> >>>>> mtd_is_eccerr() however, would be meaningful.
> >>>>> >>
> >>>> Sure I know mtd_is_bitflip() does not mean failure, but I do not think
> >>>> mtd_is_eccerr() should be here since the codes are ret < 0 and NOT
> >>>> mtd_is_bitflip().
> >>>
> >>> Yes, just drop this check, only keep ret < 0.
> >>> >>
> >> If I don't get it wrong, it should not be dropped here. Like your words,
> >> "mtd_is_bitflip() does not mean that you are reading a false buffer,
> >> but that the data has been corrected as it contained bitflips.", the
> >> data I get are valid even if mtd_is_bitflip() return true. It's correct
> >> data and it's no need to go to handle error. To me, the codes
> >> should be:
> >> if (ret < 0 && !mit_is_bitflip())
> >> [error handling]
> >
> > Please check the implementation of mtd_is_bitflip(). You'll probably
> > figure out what I am saying.
> >
> > https://elixir.bootlin.com/linux/latest/source/include/linux/mtd/mtd.h#L585
> >
>
> How about the codes as follows:
>
> for (done = 0, retlen = 0; done < size; done += retlen) {
> ret = mtd_read(..., &retlen, ...);
> if (!ret)
> continue;
> /*
> * do nothing if bitflip and ecc error occurs because whether
> * it's bitflip or ECC error, just a small number of bits flip
> * and the impact on log data is so small. The mtdpstore just
> * hands over what it gets and user can judge whether the data
> * is valid or not.
> */
> if (mtd_is_bitflip(ret)) {
> dev_warn("bitflip at....");
> continue;

I don't understand why do you check for bitflips. Bitflips have been
corrected at this stage, you just get the information that there
has been bitflips, but the data integrity is fine.

I am not against ignoring ECC errors in this case though. I would
propose:

for (...) {
if (ret < 0) {
complain;
return;
}

if (mtd_is_eccerr())
complain;
}

> } else if (mtd_is_eccerr(ret)) {
> dev_warn("eccerr at....");
> retlen = retlen == 0 ? size : retlen;
> continue;
> } else {
> dev_err("read failure at...");
> /* this zone is broken, try next one */
> return -ENEXT;
> }
> }
>

Thanks,
Miquèl