linux-kernel - Re: [PATCH BUGFIX] mtd: nand: mxc: fix obiwan error in mxc_nand_v[12]_ooblayout

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Message-ID: <20160915180605.4aed48d3@bbrezillon>
Date:   Thu, 15 Sep 2016 18:06:05 +0200
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Lothar Waßmann <LW@...O-electronics.de>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        linux-mtd@...ts.infradead.org (open list:NAND FLASH SUBSYSTEM),
        linux-kernel@...r.kernel.org (open list)
Subject: Re: [PATCH BUGFIX] mtd: nand: mxc: fix obiwan error in
 mxc_nand_v[12]_ooblayout_free() functions

Hi Lothar,

On Fri,  9 Sep 2016 16:44:11 +0200
Lothar Waßmann <LW@...O-electronics.de> wrote:

> commit a894cf6c5a82 ("mtd: nand: mxc: switch to mtd_ooblayout_ops")
> introduced a regression accessing the OOB area from the mxc_nand
> driver due to an Obiwan error in the mxc_nand_v[12]_ooblayout_free()
> functions. They report a bogus oobregion { 64, 7 } which leads to
> errors accessing bogus data when reading the oob area.
> 
> Prior to the commit the mtd-oobtest module could be run without any
> errors. With the offending commit, this test fails with results like:
> |Running mtd-oobtest
> |
> |=================================================
> |mtd_oobtest: MTD device: 5
> |mtd_oobtest: MTD device size 524288, eraseblock size 131072, page size 2048, count of eraseblocks 4, pages per eraseblock 64, OOB size 64
> |mtd_test: scanning for bad eraseblocks
> |mtd_test: scanned 4 eraseblocks, 0 are bad
> |mtd_oobtest: test 1 of 5
> |mtd_oobtest: writing OOBs of whole device
> |mtd_oobtest: written up to eraseblock 0
> |mtd_oobtest: written 4 eraseblocks
> |mtd_oobtest: verifying all eraseblocks
> |mtd_oobtest: error @addr[0x0:0x19] 0x9a -> 0x78 diff 0xe2
> |mtd_oobtest: error @addr[0x0:0x1a] 0xcc -> 0x0 diff 0xcc
> |mtd_oobtest: error @addr[0x0:0x1b] 0xe0 -> 0x85 diff 0x65
> |mtd_oobtest: error @addr[0x0:0x1c] 0x60 -> 0x62 diff 0x2
> |mtd_oobtest: error @addr[0x0:0x1d] 0x69 -> 0x45 diff 0x2c
> |mtd_oobtest: error @addr[0x0:0x1e] 0xcd -> 0xa0 diff 0x6d
> |mtd_oobtest: error @addr[0x0:0x1f] 0xf2 -> 0x60 diff 0x92
> |mtd_oobtest: error: verify failed at 0x0
> [...]
> 
> Signed-off-by: Lothar Waßmann <LW@...O-electronics.de>
> ---
>  drivers/mtd/nand/mxc_nand.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/nand/mxc_nand.c b/drivers/mtd/nand/mxc_nand.c
> index 5173fad..fdee907 100644
> --- a/drivers/mtd/nand/mxc_nand.c
> +++ b/drivers/mtd/nand/mxc_nand.c
> @@ -893,7 +893,7 @@ static int mxc_v1_ooblayout_free(struct mtd_info *mtd, int section,
>  {
>  	struct nand_chip *nand_chip = mtd_to_nand(mtd);
>  
> -	if (section > nand_chip->ecc.steps)
> +	if (section >= nand_chip->ecc.steps)
>  		return -ERANGE;

Hm, looking at the commit you're pointing to, it seems that this test
is correct (we have X + 1 free sections, where X is the number of ECC
steps).

>  
>  	if (!section) {
> @@ -943,7 +943,7 @@ static int mxc_v2_ooblayout_free(struct mtd_info *mtd, int section,
>  	struct nand_chip *nand_chip = mtd_to_nand(mtd);
>  	int stepsize = nand_chip->ecc.bytes == 9 ? 16 : 26;
>  
> -	if (section > nand_chip->ecc.steps)
> +	if (section >= nand_chip->ecc.steps)
>  		return -ERANGE;

Yep, this one is a real bug.

>  
>  	if (!section) {