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 <[email protected]>
Reviewed-by: Miquel Raynal <[email protected]>
Cc: [email protected]
---
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;
}
--
1.8.5.6
Hi Xiaoming,
Xiaoming Ni <[email protected]> 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 <[email protected]>
> Reviewed-by: Miquel Raynal <[email protected]>
> Cc: [email protected]
Still missing:
* Fixes: tag
* Wrong title prefix
On 2020/3/30 21:52, Miquel Raynal wrote:
> Hi Xiaoming,
>
> Xiaoming Ni <[email protected]> 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 <[email protected]>
>> Reviewed-by: Miquel Raynal <[email protected]>
>> Cc: [email protected]
>
> Still missing:
> * Fixes: tag
> * Wrong title prefix
>
Fixes: 1da177e4c3f41524e88 "Linux-2.6.12-rc2"
Is it described like this?
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
Hi Xiaoming,
Xiaoming Ni <[email protected]> wrote on Mon, 30 Mar 2020 22:25:36
+0800:
> On 2020/3/30 21:52, Miquel Raynal wrote:
> > Hi Xiaoming,
> >
> > Xiaoming Ni <[email protected]> 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 <[email protected]>
> >> Reviewed-by: Miquel Raynal <[email protected]>
> >> Cc: [email protected]
> >
> > 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