ping; [PATCH v4] mtd: clear cache_state to avoid writing to bad blocks repeatedly

[Xiaoming Ni]

ping

On 2020/3/31 9:31, Xiaoming Ni wrote:
> The function call process is as follows:
> 	mtd_blktrans_work()
> 	  while (1)
> 	    do_blktrans_request()
> 	      mtdblock_writesect()
> 	        do_cached_write()
> 	          write_cached_data() /*if cache_state is STATE_DIRTY*/
> 	            erase_write()
>
> write_cached_data() returns failure without modifying cache_state
> and cache_offset. So when do_cached_write() is called again,
> write_cached_data() will be called again to perform erase_write()
> on the same cache_offset.
>
> But if this cache_offset points to a bad block, erase_write() will
> always return -EIO. Writing to this mtdblk is equivalent to losing
> the current data, and repeatedly writing to the bad block.
>
> Repeatedly writing a bad block has no real benefits,
> but brings some negative effects:
> 1 Lost subsequent data
> 2 Loss of flash device life
> 3 erase_write() bad blocks are very time-consuming. For example:
> 	the function do_erase_oneblock() in chips/cfi_cmdset_0020.c or
> 	chips/cfi_cmdset_0002.c may take more than 20 seconds to return
>
> Therefore, when erase_write() returns -EIO in write_cached_data(),
> clear cache_state to avoid writing to bad blocks repeatedly.
>
> Signed-off-by: Xiaoming Ni <nixiaoming@xxxxxxxxxx>
> Reviewed-by: Miquel Raynal <miquel.raynal@xxxxxxxxxxx>
> ---
>   drivers/mtd/mtdblock.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/mtd/mtdblock.c b/drivers/mtd/mtdblock.c
> index 078e0f6..32e52d8 100644
> --- a/drivers/mtd/mtdblock.c
> +++ b/drivers/mtd/mtdblock.c
> @@ -89,8 +89,6 @@ static int write_cached_data (struct mtdblk_dev *mtdblk)
>   
>   	ret = erase_write (mtd, mtdblk->cache_offset,
>   			   mtdblk->cache_size, mtdblk->cache_data);
> -	if (ret)
> -		return ret;
>   
>   	/*
>   	 * Here we could arguably set the cache state to STATE_CLEAN.
> @@ -98,9 +96,14 @@ static int write_cached_data (struct mtdblk_dev *mtdblk)
>   	 * be notified if this content is altered on the flash by other
>   	 * means.  Let's declare it empty and leave buffering tasks to
>   	 * the buffer cache instead.
> +	 *
> +	 * If this cache_offset points to a bad block, data cannot be
> +	 * written to the device. Clear cache_state to avoid writing to
> +	 * bad blocks repeatedly.
>   	 */
> -	mtdblk->cache_state = STATE_EMPTY;
> -	return 0;
> +	if (ret == 0 || ret == -EIO)
> +		mtdblk->cache_state = STATE_EMPTY;
> +	return ret;
>   }
>   
>