linux-kernel - Re: [PATCH v3] mtd: nand_bbt: scan for next free bbt block if writing bbt fails

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Message-ID: <20160330151351.323a5333@bbrezillon>
Date:	Wed, 30 Mar 2016 15:13:51 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Kyle Roeschley <kyle.roeschley@...com>
Cc:	richard@....at, nathan.sullivan@...com, xander.huff@...com,
	linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
	computersforpeace@...il.com, dwmw2@...radead.org,
	beanhuo@...ron.com
Subject: Re: [PATCH v3] mtd: nand_bbt: scan for next free bbt block if
 writing bbt fails

Hi Kyle,

On Fri, 25 Mar 2016 17:31:16 -0500
Kyle Roeschley <kyle.roeschley@...com> wrote:

> If erasing or writing the BBT fails, we should mark the current BBT
> block as bad and use the BBT descriptor to scan for the next available
> unused block in the BBT. We should only return a failure if there isn't
> any space left.
> 
> Based on original code implemented by Jeff Westfahl
> <jeff.westfahl@...com>.
> 
> Signed-off-by: Kyle Roeschley <kyle.roeschley@...com>
> Suggested-by: Jeff Westfahl <jeff.westfahl@...com>
> ---
> This v3 is in response to comments from Brian Norris and Bean Ho on 8/26/15:
> http://lists.infradead.org/pipermail/linux-mtd/2015-August/061411.html
> 
> v3: Don't overload mtd->priv
>     Keep nand_erase_nand from erroring on protected BBT blocks
> 
> v2: Mark OOB area in each block as well as BBT
>     Avoid marking read-only, bad address, or known bad blocks as bad
> ---
>  drivers/mtd/nand/nand_base.c |  4 ++--
>  drivers/mtd/nand/nand_bbt.c  | 37 +++++++++++++++++++++++++++++++++++--
>  2 files changed, 37 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> index b6facac..9ad8a86 100644
> --- a/drivers/mtd/nand/nand_base.c
> +++ b/drivers/mtd/nand/nand_base.c
> @@ -2916,8 +2916,8 @@ int nand_erase_nand(struct mtd_info *mtd, struct erase_info *instr,
>  	/* Select the NAND device */
>  	chip->select_chip(mtd, chipnr);
>  
> -	/* Check, if it is write protected */
> -	if (nand_check_wp(mtd)) {
> +	/* Check if it is write protected, unless we're erasing BBT */
> +	if (nand_check_wp(mtd) && !allowbbt) {

Hm, will this really work. Can a write-protected device accept erase
commands?

>  		pr_debug("%s: device is write protected!\n",
>  				__func__);
>  		instr->state = MTD_ERASE_FAILED;
> diff --git a/drivers/mtd/nand/nand_bbt.c b/drivers/mtd/nand/nand_bbt.c
> index 2fbb523..01526e5 100644
> --- a/drivers/mtd/nand/nand_bbt.c
> +++ b/drivers/mtd/nand/nand_bbt.c
> @@ -662,6 +662,7 @@ static int write_bbt(struct mtd_info *mtd, uint8_t *buf,
>  			page = td->pages[chip];
>  			goto write;
>  		}
> +	next:

Please put this label at the beginning of the line and fix all the other
issues reported by checkpatch (I know we already have a 'write' label
which does not follow this rule, but let's try to avoid adding new
ones).

>  
>  		/*
>  		 * Automatic placement of the bad block table. Search direction
> @@ -787,14 +788,46 @@ static int write_bbt(struct mtd_info *mtd, uint8_t *buf,
>  		einfo.addr = to;
>  		einfo.len = 1 << this->bbt_erase_shift;
>  		res = nand_erase_nand(mtd, &einfo, 1);
> -		if (res < 0)
> +		if (res == -EIO) {
> +			/* This block is bad. Mark it as such and see if
> +			 * there's another block available in the BBT area. */
> +			int block = page >>
> +				(this->bbt_erase_shift - this->page_shift);
> +			pr_info("nand_bbt: failed to erase block %d when writing BBT\n",
> +				block);
> +			bbt_mark_entry(this, block, BBT_BLOCK_WORN);
> +
> +			res = this->block_markbad(mtd, block);

Not sure we should mark the block bad until we managed to write a new
BBT. ITOH, if we do so and the new BBT write is interrupted, it
will trigger a full BBM scan, which should be harmless on most
platforms (except those overwriting BBM with real data :-/)

> +			if (res)
> +				pr_warn("nand_bbt: error %d while marking block %d bad\n",
> +					res, block);
> +			td->pages[chip] = -1;
> +			goto next;
> +		} else if (res < 0) {
>  			goto outerr;
> +		}
>  
>  		res = scan_write_bbt(mtd, to, len, buf,
>  				td->options & NAND_BBT_NO_OOB ? NULL :
>  				&buf[len]);
> -		if (res < 0)
> +		if (res == -EIO) {
> +			/* This block is bad. Mark it as such and see if
> +			 * there's another block available in the BBT area. */
> +			int block = page >>
> +				(this->bbt_erase_shift - this->page_shift);
> +			pr_info("nand_bbt: failed to write block %d when writing BBT\n",
> +				block);
> +			bbt_mark_entry(this, block, BBT_BLOCK_WORN);
> +
> +			res = this->block_markbad(mtd, block);
> +			if (res)
> +				pr_warn("nand_bbt: error %d while marking block %d bad\n",
> +					res, block);
> +			td->pages[chip] = -1;
> +			goto next;
> +		} else if (res < 0) {
>  			goto outerr;
> +		}
>  
>  		pr_info("Bad block table written to 0x%012llx, version 0x%02X\n",
>  			 (unsigned long long)to, td->version[chip]);

Bean, Brian, can you comment on this new version. I haven't followed
the previous iterations, and would like to have your feedback before
taking a decision.

Thanks,

Boris


-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com