linux-kernel - Re: [PATCH 4.4 03/34] mtd: nand: gpmi: Fix failure when a erased page has a bitflip at BBM

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Date:   Wed, 7 Mar 2018 14:58:21 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     Boris Brezillon <boris.brezillon@...tlin.com>
CC:     Ben Hutchings <ben.hutchings@...ethink.co.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Richard Weinberger <richard@....at>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>
Subject: Re: [PATCH 4.4 03/34] mtd: nand: gpmi: Fix failure when a erased page
 has a bitflip at BBM

On Wed, Mar 07, 2018 at 09:12:36AM +0100, Boris Brezillon wrote:
>On Tue, 06 Mar 2018 21:22:30 +0000
>Ben Hutchings <ben.hutchings@...ethink.co.uk> wrote:
>
>> On Fri, 2018-03-02 at 09:50 +0100, Greg Kroah-Hartman wrote:
>> > 4.4-stable review patch.  If anyone has any objections, please let me know.
>> >
>> > ------------------
>> >
>> > From: Sascha Hauer <s.hauer@...gutronix.de>
>> >
>> >
>> > [ Upstream commit fdf2e821052958a114618a95ab18a300d0b080cb ]
>> >
>> > When erased subpages are read then the BCH decoder returns STATUS_ERASED
>> > if they are all empty, or STATUS_UNCORRECTABLE if there are bitflips.
>> > When there are bitflips, we have to set these bits again to show the
>> > upper layers a completely erased page. When a bitflip happens in the
>> > exact byte where the bad block marker is, then this byte is swapped
>> > with another byte in block_mark_swapping(). The correction code then
>> > detects a bitflip in another subpage and no longer corrects the bitflip
>> > where it really happens.
>> [...]
>>
>> This seesm to be a bug fix for commit bd2e778c9ee3 "gpmi-nand: Handle
>> ECC Errors in erased pages".  That's not in 4.4 so the bug fix is not
>> needed, though it doesn't appear to do any harm.
>
>I wonder why the fix was backported to stable releases in the first
>place. AFAICS, there's no Cc-stable or Fixes tag in the original
>commit. It's probably something in the backport-to-stable process I'm
>not aware of.

It's an attempt to mine kernel commits for commits that should go into
stable trees but were not marked as such.

Thanks again for the review!

-- 

Thanks,
Sasha