linux-ext4 - Re: [PATCH] ext4: Ensure zeroout blocks have no dirty metadata

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Date:	Tue, 29 Dec 2009 09:56:29 -0800
From:	Curt Wohlgemuth <curtw@...gle.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: Ensure zeroout blocks have no dirty metadata

On Fri, Dec 18, 2009 at 3:49 AM, Aneesh Kumar K.V
<aneesh.kumar@...ux.vnet.ibm.com> wrote:
> On Thu, Dec 10, 2009 at 09:28:28AM -0800, Curt Wohlgemuth wrote:
>> This fixes a bug in which new blocks returned from an extent created with
>> ext4_ext_zeroout() can have dirty metadata still associated with them.
>>
>>       Signed-off-by: Curt Wohlgemuth <curtw@...gle.com>
>> ---
>>
>> This is for the problem I reported on 23 Nov ("Bug in extent zeroout: blocks
>> not marked as new").  I'm not seeing the corruption with this fix that I was
>> seeing without it.
>>
>> diff -uprN orig/fs/ext4/extents.c new/fs/ext4/extents.c
>> --- orig/fs/ext4/extents.c    2009-12-09 15:09:25.000000000 -0800
>> +++ new/fs/ext4/extents.c     2009-12-09 15:09:37.000000000 -0800
>> @@ -2474,9 +2474,21 @@ static int ext4_ext_zeroout(struct inode
>>               submit_bio(WRITE, bio);
>>               wait_for_completion(&event);
>>
>> -             if (test_bit(BIO_UPTODATE, &bio->bi_flags))
>> +             /* On success, we need to insure all metadata associated
>> +              * with each of these blocks is unmapped. */
>> +             if (test_bit(BIO_UPTODATE, &bio->bi_flags)) {
>> +                     sector_t block = ee_pblock;
>> +
>>                       ret = 0;
>> -             else {
>> +                     done = 0;
>> +                     while (done < len) {
>> +                             unmap_underlying_metadata(inode->i_sb->s_bdev,
>> +                                                       block);
>> +
>> +                             done++;
>> +                             block++;
>> +                     }
>> +             } else {
>>                       ret = -EIO;
>>                       break;
>>               }
>
> a) We are zeroing out 'done' blocks but you are unmapping 'len' blocks ?
> b) We are already doing a unmap in mpage_da_map_blocks so i guess
>   what you want is to unmap the extra block allocated
> c) ee_pblock is in 512 byte units so the block number is wrong.
>
> how about the patch below ?

Thanks for pointing out the arithmetic problems in my patch.  Yours
below looks good to me.
Curt


>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 3a7928f..f9a735f 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -3023,6 +3023,14 @@ out:
>        return err;
>  }
>
> +static void unmap_underlying_metadata_blocks(struct block_device *bdev,
> +                       sector_t block, int count)
> +{
> +       int i;
> +       for (i = 0; i < count; i++)
> +                unmap_underlying_metadata(bdev, block + i);
> +}
> +
>  static int
>  ext4_ext_handle_uninitialized_extents(handle_t *handle, struct inode *inode,
>                        ext4_lblk_t iblock, unsigned int max_blocks,
> @@ -3098,6 +3106,18 @@ out:
>        } else
>                allocated = ret;
>        set_buffer_new(bh_result);
> +       /*
> +        * if we allocated more blocks than requested
> +        * we need to make sure we unmap the extra block
> +        * allocated. The actual needed block will get
> +        * unmapped later when we find the buffer_head marked
> +        * new.
> +        */
> +       if (allocated > max_blocks) {
> +               unmap_underlying_metadata_blocks(inode->i_sb->s_bdev,
> +                                       newblock + max_blocks,
> +                                       allocated - max_blocks);
> +       }
>  map_out:
>        set_buffer_mapped(bh_result);
>  out1:
>
>
>
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