Re: [f2fs-dev] [PATCH v2 3/3] f2fs: fix to zero data after EOF for compressed file correctly

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

Jaegeuk, sure, let me change the order.

On 8/5/25 10:42, Jaegeuk Kim wrote:
> Chao, it seems you made a clean up before this? Can you post it first?
> 
> On 08/04, Chao Yu wrote:
>> generic/091 may fail, then it bisects to the bad commit ba8dac350faf
>> ("f2fs: fix to zero post-eof page").
>>
>> What will cause generic/091 to fail is something like below Testcase #1:
>> 1. write 16k as compressed blocks
>> 2. truncate to 12k
>> 3. truncate to 20k
>> 4. verify data in range of [12k, 16k], however data is not zero as
>> expected
>>
>> Script of Testcase #1
>> mkfs.f2fs -f -O extra_attr,compression /dev/vdb
>> mount -t f2fs -o compress_extension=* /dev/vdb /mnt/f2fs
>> dd if=/dev/zero of=/mnt/f2fs/file bs=12k count=1
>> dd if=/dev/random of=/mnt/f2fs/file bs=4k count=1 seek=3 conv=notrunc
>> sync
>> truncate -s $((12*1024)) /mnt/f2fs/file
>> truncate -s $((20*1024)) /mnt/f2fs/file
>> dd if=/mnt/f2fs/file of=/mnt/f2fs/data bs=4k count=1 skip=3
>> od /mnt/f2fs/data
>> umount /mnt/f2fs
>>
>> Analisys:
>> in step 2), we will redirty all data pages from #0 to #3 in compressed
>> cluster, and zero page #3,
>> in step 3), f2fs_setattr() will call f2fs_zero_post_eof_page() to drop
>> all page cache post eof, includeing dirtied page #3,
>> in step 4) when we read data from page #3, it will decompressed cluster
>> and extra random data to page #3, finally, we hit the non-zeroed data
>> post eof.
>>
>> However, the commit ba8dac350faf ("f2fs: fix to zero post-eof page") just
>> let the issue be reproduced easily, w/o the commit, it can reproduce this
>> bug w/ below Testcase #2:
>> 1. write 16k as compressed blocks
>> 2. truncate to 8k
>> 3. truncate to 12k
>> 4. truncate to 20k
>> 5. verify data in range of [12k, 16k], however data is not zero as
>> expected
>>
>> Script of Testcase #2
>> mkfs.f2fs -f -O extra_attr,compression /dev/vdb
>> mount -t f2fs -o compress_extension=* /dev/vdb /mnt/f2fs
>> dd if=/dev/zero of=/mnt/f2fs/file bs=12k count=1
>> dd if=/dev/random of=/mnt/f2fs/file bs=4k count=1 seek=3 conv=notrunc
>> sync
>> truncate -s $((8*1024)) /mnt/f2fs/file
>> truncate -s $((12*1024)) /mnt/f2fs/file
>> truncate -s $((20*1024)) /mnt/f2fs/file
>> echo 3 > /proc/sys/vm/drop_caches
>> dd if=/mnt/f2fs/file of=/mnt/f2fs/data bs=4k count=1 skip=3
>> od /mnt/f2fs/data
>> umount /mnt/f2fs
>>
>> Anlysis:
>> in step 2), we will redirty all data pages from #0 to #3 in compressed
>> cluster, and zero page #2 and #3,
>> in step 3), we will truncate page #3 in page cache,
>> in step 4), expand file size,
>> in step 5), hit random data post eof w/ the same reason in Testcase #1.
>>
>> Root Cause:
>> In f2fs_truncate_partial_cluster(), after we truncate partial data block
>> on compressed cluster, all pages in cluster including the one post eof
>> will be dirtied, after another tuncation, dirty page post eof will be
>> dropped, however on-disk compressed cluster is still valid, it includes
>> invalid data post eof, result in exposing previous data post eof while
>> reading.
>>
>> Fix:
>> In f2fs_truncate_partial_cluster(), let change as below to fix:
>> - call filemap_write_and_wait_range() to flush dirty page
>> - call truncate_pagecache() to drop pages or zero partial page post eof
>> - call f2fs_do_truncate_blocks() to truncate non-compress cluster to
>>   last vali block
>>
>> Fixes: 3265d3db1f16 ("f2fs: support partial truncation on compressed inode")
>> Reported-by: Jan Prusakowski <jprusakowski@google.com>
>> Signed-off-by: Chao Yu <chao@kernel.org>
>> ---
>> v2:
>> - should dirty & flush all pages in cluster and truncate blocks post eof
>> later
>>  fs/f2fs/compress.c | 20 ++++++++++++++------
>>  1 file changed, 14 insertions(+), 6 deletions(-)
>>
>> diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
>> index e37a7ed801e5..6ad8d3bc6df7 100644
>> --- a/fs/f2fs/compress.c
>> +++ b/fs/f2fs/compress.c
>> @@ -1245,17 +1245,25 @@ int f2fs_truncate_partial_cluster(struct inode *inode, u64 from, bool lock)
>>  	for (i = (1 << log_cluster_size) - 1; i >= 0; i--) {
>>  		struct folio *folio = page_folio(rpages[i]);
>>  		loff_t start = (loff_t)folio->index << PAGE_SHIFT;
>> +		loff_t offset = from > start ? from - start : 0;
>>  
>> -		if (from > start) {
>> -			folio_zero_segment(folio, from - start,
>> -					folio_size(folio));
>> +		folio_zero_segment(folio, offset, folio_size(folio));
>> +
>> +		if (from >= start)
>>  			break;
>> -		}
>> -		folio_zero_segment(folio, 0, folio_size(folio));
>>  	}
>>  
>>  	f2fs_compress_write_end(inode, fsdata, start_idx, true);
>> -	return 0;
>> +
>> +	err = filemap_write_and_wait_range(inode->i_mapping,
>> +			round_down(from, 1 << log_cluster_size << PAGE_SHIFT),
>> +			LLONG_MAX);
>> +	if (err)
>> +		return err;
>> +
>> +	truncate_pagecache(inode, from);
>> +
>> +	return f2fs_do_truncate_blocks(inode, round_up(from, PAGE_SIZE), lock);
>>  }
>>  
>>  static int f2fs_write_compressed_pages(struct compress_ctx *cc,
>> -- 
>> 2.49.0



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