linux-kernel - Re: [PATCH v3] mtd:fix cache_state to avoid writing to bad blocks repeatedly

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Date:   Mon, 30 Mar 2020 16:55:47 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Xiaoming Ni <nixiaoming@...wei.com>
Cc:     <richard@....at>, <vigneshr@...com>, <gregkh@...uxfoundation.org>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <wangle6@...wei.com>, <zhangweimin12@...wei.com>,
        <yebin10@...wei.com>, <houtao1@...wei.com>, <stable@...nel.org>
Subject: Re: [PATCH v3] mtd:fix cache_state to avoid writing to bad blocks
 repeatedly

Hi Xiaoming,

Xiaoming Ni <nixiaoming@...wei.com> wrote on Mon, 30 Mar 2020 22:25:36
+0800:

> On 2020/3/30 21:52, Miquel Raynal wrote:
> > Hi Xiaoming,
> > 
> > Xiaoming Ni <nixiaoming@...wei.com> wrote on Mon, 30 Mar 2020 21:45:25
> > +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>
> >> Cc: stable@...r.kernel.org  
> > 
> > Still missing:
> > * Fixes: tag
> > * Wrong title prefix
> >   
> 
> Fixes: 	1da177e4c3f41524e88 "Linux-2.6.12-rc2"
> 
> Is it described like this?

The way to describe a commit is:

Fixes: 1da177e4c3f4 ("Linux-...")

But it is too old to be pointed, just drop both Fixes/Cc tags and just
fix the title please.

> 
> Do I need to go to
> https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git
> to trace back the older commit records?
> 
> Thanks
> Xiaoming Ni
> 
> 
> 
> 

Thanks,
Miquèl