linux-kernel - Re: [PATCH v2] mtd:clear cache_state to avoid writing to bad blocks repeatedly

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Message-ID: <20200330152539.1395e456@xps13>
Date:   Mon, 30 Mar 2020 15:25:39 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Xiaoming Ni <nixiaoming@...wei.com>
Cc:     <richard@....at>, <vigneshr@...com>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <wangle6@...wei.com>, <zhangweimin12@...wei.com>,
        <yebin10@...wei.com>, <houtao1@...wei.com>
Subject: Re: [PATCH v2] mtd:clear cache_state to avoid writing to bad blocks
 repeatedly

Hi Xiaoming,

Xiaoming Ni <nixiaoming@...wei.com> wrote on Mon, 30 Mar 2020 21:11:09
+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 blocks repeatedly.
> 
> Signed-off-by: Xiaoming Ni <nixiaoming@...wei.com>
> Reviewed-by: Miquel Raynal <miquel.raynal@...tlin.com>

The title is still wrong.

And you'll need a Fixes tag as well. Cc: stable is also a good idea.

Thanks,
Miquèl