On 2018年05月15日 00:52, David Sterba wrote:
> On Mon, May 14, 2018 at 03:02:10PM +0800, Qu Wenruo wrote:
>> As btrfs(5) specified:
>>
>> 	Note
>> 	If nodatacow or nodatasum are enabled, compression is disabled.
>>
>> If NODATASUM or NODATACOW set, we should not compress the extent.
>>
>> And in fact, we have bug report about corrupted compressed extent
>> leading to memory corruption in mail list.
> 
> Link please.
> 
>> Although it's mostly buggy lzo implementation causing the problem, btrfs
>> still needs to be fixed to meet the specification.
> 
> That's very vague, what's the LZO bug? If the input is garbage and lzo
> decompression cannot decompress it, it's not a lzo bug.

Still digging.
Would update this content in next version.

> 
>> Reported-by: James Harvey <jamespharvey20@gmail.com>
>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>> ---
>>  fs/btrfs/inode.c | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
>> index d241285a0d2a..dbef3f404559 100644
>> --- a/fs/btrfs/inode.c
>> +++ b/fs/btrfs/inode.c
>> @@ -396,6 +396,14 @@ static inline int inode_need_compress(struct inode *inode, u64 start, u64 end)
>>  {
>>  	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
>>  
>> +	/*
>> +	 * Btrfs doesn't support compression without csum or CoW.
>> +	 * This should have the highest priority.
>> +	 */
>> +	if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW ||
>> +	    BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)
>> +		return 0;
> 
> This is also the wrong place to fix that, NODATASUM or NODATACOW inode
> should never make it to compress_file_range (that calls
> inode_need_compress).

Nope, in run_delalloc_range(), we calls inode_need_compress() to
determine if we goes to normal cow routine or goes to async routine
(compression).

So inode_need_compress() looks like a pretty valid location.

Just mount with nodatasum and create an inode, then remount to
datasum,compress, write something to that inode, you could hit the behavior.

Thanks,
Qu

> 
>> +
>>  	/* force compress */
>>  	if (btrfs_test_opt(fs_info, FORCE_COMPRESS))
>>  		return 1;
>> -- 
>> 2.17.0
>>
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