Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 6 Feb 2020 16:45:59 +0100
From:   Miquel Raynal <mraynal@kernel.org>
To:     liaoweixiong <liaoweixiong@allwinnertech.com>
Cc:     Kees Cook <keescook@chromium.org>,
        Anton Vorontsov <anton@enomsg.org>,
        Colin Cross <ccross@android.com>,
        Tony Luck <tony.luck@intel.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Rob Herring <robh@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mtd@lists.infradead.org
Subject: Re: [PATCH v1 11/11] mtd: new support oops logger based on
 pstore/blk
Message-ID: <20200206164559.59c5eb6a@xps13>
In-Reply-To: <e135f947-226f-8dd0-b328-fb87c5064914@allwinnertech.com>
References: <1579482233-2672-1-git-send-email-liaoweixiong@allwinnertech.com>
        <1579482233-2672-12-git-send-email-liaoweixiong@allwinnertech.com>
        <20200120110306.32e53fd8@xps13>
        <27226590-379c-8784-f461-f5d701015611@allwinnertech.com>
        <20200121094802.61f8cb4d@xps13>
        <2c6000b1-ae25-564b-911a-2879e9c244b2@allwinnertech.com>
        <20200122184114.125b42c8@xps13>
        <e135f947-226f-8dd0-b328-fb87c5064914@allwinnertech.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi liao,

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

> hi Miquel Raynal,
>=20
> On 2020/1/23 AM 1:41, Miquel Raynal wrote:
> > Hello,
> >=20
> >  =20
> >>>>>> +/*
> >>>>>> + * 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 =3D &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 =3D mtd_read(cxt->mtd, off, size, &retlen, (u_char *)buf);
> >>>>>> +	if ((ret < 0 && !mtd_is_bitflip(ret)) || size !=3D retlen)  { =20
> >>>>>
> >>>>> IIRC size !=3D retlen does not mean it failed, but that you should
> >>>>> continue reading after retlen bytes, no? =20
> >>>>>     >> =20
> >>>> Yes, you are right. I will fix it. Thanks. =20
> >>>>   >>>>> Also, mtd_is_bitflip() does not mean that you are reading a =
false =20
> >>>>> buffer, but that the data has been corrected as it contained bitfli=
ps.
> >>>>> mtd_is_eccerr() however, would be meaningful. =20
> >>>>>     >> =20
> >>>> Sure I know mtd_is_bitflip() does not mean failure, but I do not thi=
nk
> >>>> mtd_is_eccerr() should be here since the codes are ret < 0 and NOT
> >>>> mtd_is_bitflip(). =20
> >>>
> >>> Yes, just drop this check, only keep ret < 0. =20
> >>>    >> =20
> >> If I don't get it wrong, it should not	 be dropped here. Like your wor=
ds,
> >> "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] =20
> >=20
> > Please check the implementation of mtd_is_bitflip(). You'll probably
> > figure out what I am saying.
> >=20
> > https://elixir.bootlin.com/linux/latest/source/include/linux/mtd/mtd.h#=
L585
> >  =20
>=20
> How about the codes as follows:
>=20
> for (done =3D 0, retlen =3D 0; done < size; done +=3D retlen) {
> 	ret =3D 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;
	}
	=09
> 	} else if (mtd_is_eccerr(ret)) {
> 		dev_warn("eccerr at....");
> 		retlen =3D retlen =3D=3D 0 ? size : retlen;
> 		continue;
> 	} else {
> 		dev_err("read failure at...");
> 		/* this zone is broken, try next one */
> 		return -ENEXT;
> 	}
> }
>=20


Thanks,
Miqu=C3=A8l