ping; [PATCH v4] mtd: clear cache_state to avoid writing to bad blocks repeatedly

[Xiaoming Ni]

ping

On 2020/3/31 9:31, 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 <nixiaom...@huawei.com>
Reviewed-by: Miquel Raynal <miquel.ray...@bootlin.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..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;
  }