Re: [f2fs-dev] [PATCH v2 2/2] f2fs: fix infinite loop in __insert_extent_tree()

[Chao Yu]

On 9/16/25 15:09, wangzijie wrote:
>> On 9/16/25 13:22, wangzijie wrote:
>>>> On 09/15, wangzijie wrote:
>>>>> When we get wrong extent info data, and look up extent_node in rb tree,
>>>>> it will cause infinite loop (CONFIG_F2FS_CHECK_FS=n). Avoiding this by
>>>>> return NULL.
>>>>
>>>> This is the exact buggy case which we should fix the original one. Have
>>>> you seen this error? In that case, can we consider writing some kernel
>>>> message and handle the error properly?
>>>
>>> Hi Jaegeuk,
>>> The original one is the bug I mentioned in the first patch of this patch set
>>> ("f2fs: fix zero-sized extent for precache extents"). 
>>
>> Zijie,
>>
>> Did you suffer this problem in product? right?
> 
> Hi Chao,
> Yes, and I can confirm that infinite loop cases I suffered are caused by the bug I
> mentioned in the first patch of this patch set. But I'm not sure if there are
> other cases that can cause this infinite loop.
> 
>>>
>>> When we use a wrong extent_info(zero-sized) to do update, and there exists a
>>> extent_node which has same fofs as the wrong one, we will skip "invalidate all extent
>>> nodes in range [fofs, fofs + len - 1]"(en->ei.fofs = end = tei->fofs + tei->len = tei->fofs),
>>> which cause the infinite loop in __insert_extent_tree().
>>>
>>> So we can add f2fs_bug_on() when there occurs zero-sized extent
>>> in f2fs_update_read_extent_cache_range(), and give up this zero-sized
>>> extent update to handle other unknown buggy cases. Do you think this will be better?
>>>
>>> And do we need to solve this infinite loop?
>>
>> IMO, it's worth to end such loop if there is any corrupted extent in rbtree to
>> avoid kernel hang, no matter it is caused by software bug or hardware flaw
>> potentially.
>>
>> Thanks,
> 
> And do you think we need this?
> "add f2fs_bug_on() when there occurs zero-sized extent in f2fs_update_read_extent_cache_range(),
> and give up this zero-sized extent update to handle other unknown buggy cases".

Oh, I was testing below patch..., does this what you want to do?

I think we can keep all your patches, and appending below patch to detect any
potential cases who will update a zero-sized extent.