Re: [f2fs-dev] [bug report]WARNING: CPU: 22 PID: 44011 at fs/iomap/iter.c:51 iomap_iter+0x32b observed with blktests zbd/010

[Chao Yu <chao@kernel.org>]

On 2024/3/25 14:56, Shinichiro Kawasaki wrote:
> On Mar 25, 2024 / 11:06, Chao Yu wrote:
>> On 2024/3/25 10:14, Shinichiro Kawasaki wrote:
>>> On Mar 24, 2024 / 20:13, Chao Yu wrote:
>>> ...
>>>> Hi Shinichiro,
>>>>
>>>> Can you please check below diff? IIUC, for the case: f2fs_map_blocks()
>>>> returns zero blkaddr in non-primary device, which is a verified valid
>>>> block address, we'd better to check m_flags & F2FS_MAP_MAPPED instead
>>>> of map.m_pblk != NULL_ADDR to decide whether tagging IOMAP_MAPPED flag
>>>> or not.
>>>>
>>>> ---
>>>>    fs/f2fs/data.c | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>>> index 6f66e3e4221a..41a56d4298c8 100644
>>>> --- a/fs/f2fs/data.c
>>>> +++ b/fs/f2fs/data.c
>>>> @@ -4203,7 +4203,7 @@ static int f2fs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>>>>    	if (WARN_ON_ONCE(map.m_pblk == COMPRESS_ADDR))
>>>>    		return -EINVAL;
>>>>
>>>> -	if (map.m_pblk != NULL_ADDR) {
>>>> +	if (map.m_flags & F2FS_MAP_MAPPED) {
>>>>    		iomap->length = blks_to_bytes(inode, map.m_len);
>>>>    		iomap->type = IOMAP_MAPPED;
>>>>    		iomap->flags |= IOMAP_F_MERGED;
>>>>
>>>
>>> Thanks Chao, I confirmed that the diff above avoids the WARN and zbd/010
>>> failure. From that point of view, it looks good.
>>
>> Thank you for the confirmation. :)
>>
>>>
>>> One thing I noticed is that the commit message of 8d3c1fa3fa5ea ("f2fs:
>>> don't rely on F2FS_MAP_* in f2fs_iomap_begin") says that f2fs_map_blocks()
>>> might be setting F2FS_MAP_* flag on a hole, and that's why the commit
>>> avoided the F2FS_MAP_MAPPED flag check. So I was not sure if it is the
>>> right thing to reintroduce the flag check.
>>
>> I didn't see such logic in previous f2fs_map_blocks(, F2FS_GET_BLOCK_DIO) codebase,
>> I doubt it hits the same case: map.m_pblk is valid zero blkaddr which locates in
>> the head of secondary device? What do you think?
>>
>> Quoted commit message from 8d3c1fa3fa5ea:
>>
>> When testing with a mixed zoned / convention device combination, there
>> are regular but not 100% reproducible failures in xfstests generic/113
>> where the __is_valid_data_blkaddr assert hits due to finding a hole.
>>
>> Previous code:
>>
>> -	if (map.m_flags & (F2FS_MAP_MAPPED | F2FS_MAP_UNWRITTEN)) {
>> -		iomap->length = blks_to_bytes(inode, map.m_len);
>> -		if (map.m_flags & F2FS_MAP_MAPPED) {
>> -			iomap->type = IOMAP_MAPPED;
>> -			iomap->flags |= IOMAP_F_MERGED;
>> -		} else {
>> -			iomap->type = IOMAP_UNWRITTEN;
>> -		}
>> -		if (WARN_ON_ONCE(!__is_valid_data_blkaddr(map.m_pblk)))
>> -			return -EINVAL;
> 
> Hmm, I can agree with your guess. Let me add two more points:
> 
> 1) The commit message says that the generic/113 failure was not 100% recreated.
>     So it was difficult to confirm that the commit avoided the failure, probably.
> 
> 2) I ran zbd/010 using the kernel just before the commit 8d3c1fa3fa5ea, and
>     observed the WARN in the hunk you quoted above.
> 
>       WARNING: CPU: 1 PID: 1035 at fs/f2fs/data.c:4164 f2fs_iomap_begin+0x19e/0x1b0 [f2fs]
> 
>     So, it implies that the WARN observed xfstests generic/113 has same failure
>     scenario as blktests zbd/010, probably.

Yup,

> 
> 
> Based on these guesses, I think your fix diff is reasonable. If you post it as a
> formal patch, feel free to add my:
> 
> Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>

Thank you for the test!

I've submitted a formal patch, let me know, if you have any comments on it, or want
to update it.

https://lore.kernel.org/linux-f2fs-devel/20240325152623.797099-1-chao@kernel.org/

Thanks,


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