linux-kernel - Re: [PATCH 4/9] mtd: nand: qcom: fix null pointer access for erased buffer detection

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Date:   Mon, 23 Apr 2018 11:59:46 +0530
From:   Abhishek Sahu <absahu@...eaurora.org>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Archit Taneja <architt@...eaurora.org>,
        Richard Weinberger <richard@....at>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Marek Vasut <marek.vasut@...il.com>,
        linux-mtd@...ts.infradead.org,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Andy Gross <andy.gross@...aro.org>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH 4/9] mtd: nand: qcom: fix null pointer access for erased
 buffer detection

On 2018-04-22 21:55, Miquel Raynal wrote:
> Hi Abhishek,
> 
> On Thu, 12 Apr 2018 12:24:16 +0530, Abhishek Sahu
> <absahu@...eaurora.org> wrote:
> 
>> On 2018-04-10 14:42, Miquel Raynal wrote:
>> > Hi Abhishek,
>> > > On Wed,  4 Apr 2018 18:12:20 +0530, Abhishek Sahu
>> > <absahu@...eaurora.org> wrote:
>> > >> parse_read_errors can be called with only oob buf also in which
>> >> case data_buf will be NULL.  If data_buf is NULL, then don’t
>> >> treat this page as completely erased in case of ECC uncorrectable
>> >> error.
>> >> >> Signed-off-by: Abhishek Sahu <absahu@...eaurora.org>
>> >> ---
>> >>  drivers/mtd/nand/qcom_nandc.c | 7 +++++--
>> >>  1 file changed, 5 insertions(+), 2 deletions(-)
>> >> >> diff --git a/drivers/mtd/nand/qcom_nandc.c >> b/drivers/mtd/nand/qcom_nandc.c
>> >> index 57c16a6..0ebcc55 100644
>> >> --- a/drivers/mtd/nand/qcom_nandc.c
>> >> +++ b/drivers/mtd/nand/qcom_nandc.c
>> >> @@ -1607,9 +1607,11 @@ static int parse_read_errors(struct >> qcom_nand_host *host, u8 *data_buf,
>> >>  			if (host->bch_enabled) {
>> >>  				erased = (erased_cw & ERASED_CW) == ERASED_CW ?
>> >>  					 true : false;
>> > > Why the parse_read_errors() function could not be called without
>> > data_buf when using BCH? Are you sure the situation can only happen
>> > without it?
>> >
>>    host->bch_enabled case is different where controller itself tells
>>    regarding erased page in status register.
>> 
>> > Would the following apply here too, with a:
>> >
>>   erased_chunk_check_and_fixup will be used only for 4 bit RS ECC
>>   code in which there is no support from HW for erased page detection
>>   and we need to check few data bytes value.
> 
> So please explain this with a comment.
> 
> Thanks,
> Miquèl

  Sure Miquel.
  I will do the same and update the patch with more comments.

  Thanks,
  Abhishek