[PATCH] mtd:clear cache_state to avoid writing to bad clocks repeatedly

[PATCH] mtd:clear cache_state to avoid writing to bad clocks repeatedly

[Xiaoming Ni]

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 clocks repeatedly.

Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
---
 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..98c25d6 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 clocks repeatedly
 	 */
-	mtdblk->cache_state = STATE_EMPTY;
-	return 0;
+	if (ret == 0 || ret == -EIO)
+		mtdblk->cache_state = STATE_EMPTY;
+	return ret;
 }
 
 
-- 
1.8.5.6

Re: [PATCH] mtd:clear cache_state to avoid writing to bad clocks repeatedly

[Miquel Raynal]

Hi Xiaoming,

Xiaoming Ni <nixiaoming@huawei.com> wrote on Sat, 28 Mar 2020 21:01:17
+0800:

> 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 clocks repeatedly.

                                            blocks

> 
> Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
> ---
>  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..98c25d6 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

Can you start your sentences with a capital letter please?

	 * If

> +	 * data cannot be written to the device.
> +	 * clear cache_state to avoid writing to bad clocks repeatedly

	 * Clear

And also please break your lines à 80, not 70.

>  	 */
> -	mtdblk->cache_state = STATE_EMPTY;
> -	return 0;
> +	if (ret == 0 || ret == -EIO)
> +		mtdblk->cache_state = STATE_EMPTY;
> +	return ret;
>  }
>  
>  

Otherwise looks good to me.

With the above addressed:

Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>


Thanks,
Miquèl

Re: [PATCH] mtd:clear cache_state to avoid writing to bad clocks repeatedly

[Xiaoming Ni]

On 2020/3/30 15:53, Miquel Raynal wrote:
> Hi Xiaoming,
> 
> Xiaoming Ni <nixiaoming@huawei.com> wrote on Sat, 28 Mar 2020 21:01:17
> +0800:
> 
>> The function call process is as follows:
>> 	mtd_blktrans_work()
>> 	  while (1)
....

>> +	 *
>> +	 * if this cache_offset points to a bad block
> 
> Can you start your sentences with a capital letter please?
> 
> 	 * If
> 
>> +	 * data cannot be written to the device.
>> +	 * clear cache_state to avoid writing to bad clocks repeatedly
> 
> 	 * Clear
> 
> And also please break your lines à 80, not 70.
> 
>>   	 */
>> -	mtdblk->cache_state = STATE_EMPTY;
>> -	return 0;
>> +	if (ret == 0 || ret == -EIO)
>> +		mtdblk->cache_state = STATE_EMPTY;
Should I add a warning print for EIO here


>> +	return ret;
>>   }
>>   
>>   
> 
> Otherwise looks good to me.
> 
> With the above addressed:
> 
> Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
> 
> 
> Thanks,
> Miquèl
> 
> .

Thanks for your advice, I will send v2 patch later

Thanks,
Xiaoming Ni

Re: [PATCH] mtd:clear cache_state to avoid writing to bad clocks repeatedly

[Miquel Raynal]

Hi Xiaoming,

Xiaoming Ni <nixiaoming@huawei.com> wrote on Mon, 30 Mar 2020 16:44:29
+0800:

> On 2020/3/30 15:53, Miquel Raynal wrote:
> > Hi Xiaoming,
> > 
> > Xiaoming Ni <nixiaoming@huawei.com> wrote on Sat, 28 Mar 2020 21:01:17
> > +0800:
> >   
> >> The function call process is as follows:
> >> 	mtd_blktrans_work()
> >> 	  while (1)  
> ....
> 
> >> +	 *
> >> +	 * if this cache_offset points to a bad block  
> > 
> > Can you start your sentences with a capital letter please?
> > 
> > 	 * If
> >   
> >> +	 * data cannot be written to the device.
> >> +	 * clear cache_state to avoid writing to bad clocks repeatedly  
> > 
> > 	 * Clear
> > 
> > And also please break your lines à 80, not 70.
> >   
> >>   	 */
> >> -	mtdblk->cache_state = STATE_EMPTY;
> >> -	return 0;
> >> +	if (ret == 0 || ret == -EIO)
> >> +		mtdblk->cache_state = STATE_EMPTY;  
> Should I add a warning print for EIO here

I don't think so.

Thanks,
Miquèl

Re: [PATCH] mtd:clear cache_state to avoid writing to bad clocks repeatedly

[Miquel Raynal]

Hi Xiaoming,

Xiaoming Ni <nixiaoming@huawei.com> wrote on Sat, 28 Mar 2020 21:01:17
+0800:

Please also fix the title.

	"mtd: clear ..."


Thanks,
Miquèl