linux-kernel - Re: [PATCH v4] mtd: clear cache_state to avoid writing to bad blocks repeatedly

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Message-ID: <045c988f-4106-1c5c-f33a-8c2617eddbb1@huawei.com>
Date:   Tue, 31 Mar 2020 19:06:28 +0800
From:   Xiaoming Ni <nixiaoming@...wei.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     <miquel.raynal@...tlin.com>, <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 v4] mtd: clear cache_state to avoid writing to bad blocks
 repeatedly

On 2020/3/31 18:05, Greg KH wrote:
> On Tue, Mar 31, 2020 at 09:31:59AM +0800, 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@...wei.com>
>> Reviewed-by: Miquel Raynal <miquel.raynal@...tlin.com>
>> ---
>>   drivers/mtd/mtdblock.c | 11 +++++++----
>>   1 file changed, 7 insertions(+), 4 deletions(-)
> 
> $ ./scripts/get_maintainer.pl --file drivers/mtd/mtdblock.c
> Miquel Raynal <miquel.raynal@...tlin.com> (maintainer:MEMORY TECHNOLOGY DEVICES (MTD))
> Richard Weinberger <richard@....at> (maintainer:MEMORY TECHNOLOGY DEVICES (MTD))
> Vignesh Raghavendra <vigneshr@...com> (maintainer:MEMORY TECHNOLOGY DEVICES (MTD))
> linux-mtd@...ts.infradead.org (open list:MEMORY TECHNOLOGY DEVICES (MTD))
> linux-kernel@...r.kernel.org (open list)
> 
> 
> No where on there is my name/email, so why am I getting these?
> 
> confused,
> 
> greg k-h

At v3, I added Cc: stable@...r.kernel.org and emailed you,
At v4, Cc: stable@...r.kernel.org was deleted, but forgot to remove you 
from the recipient list
I'm very sorry to bother you
Thanks
Xiaoming Ni