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

[Chao Yu <chao@kernel.org>]

On 9/16/25 16:26, wangzijie wrote:
>> 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.
>>
>> >From 439d61ef3715fafa5c9f2d1b7f8026cdd2564ca7 Mon Sep 17 00:00:00 2001
>> From: Chao Yu <chao@kernel.org>
>> Date: Tue, 16 Sep 2025 11:52:30 +0800
>> Subject: [PATCH] f2fs: add sanity check on ei.len in
>> __update_extent_tree_range()
>>
>> Add a sanity check in __update_extent_tree_range() to detect any
>> zero-sized extent update.
>>
>> Signed-off-by: Chao Yu <chao@kernel.org>
>> ---
>> fs/f2fs/extent_cache.c | 9 +++++++++
>> 1 file changed, 9 insertions(+)
>>
>> diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c
>> index 199c1e7a83ef..9544323767be 100644
>> --- a/fs/f2fs/extent_cache.c
>> +++ b/fs/f2fs/extent_cache.c
>> @@ -664,6 +664,15 @@ static void __update_extent_tree_range(struct inode *inode,
>> 	if (!et)
>> 		return;
>>
>> +	if (unlikely(len == 0)) {
>> +		f2fs_bug_on(sbi, 1);
>> +		f2fs_err_ratelimited(sbi, "%s: extent len is zero, type: %d, "
>> +			"extent [%u, %u, %u], age [%llu, %llu]",
>> +			__func__, type, tei->fofs, tei->blk, tei->len,
>> +			tei->age, tei->last_blocks);
>> +		return;
>> +	}
>> +
>> 	if (type == EX_READ)
>> 		trace_f2fs_update_read_extent_tree_range(inode, fofs, len,
>> 						tei->blk, 0);
>> -- 
>> 2.49.0
> 
> Yes, that's exactly what I want to do.
> Maybe we should relocate f2fs_bug_on()?
> 
> 	if (unlikely(len == 0)) {
> 		f2fs_err_ratelimited(sbi, "%s: extent len is zero, type: %d, "
> 			"extent [%u, %u, %u], age [%llu, %llu]",
> 			__func__, type, tei->fofs, tei->blk, tei->len,
> 			tei->age, tei->last_blocks);
> 		f2fs_bug_on(sbi, 1);
> 		return;
> 	}

Yeah, looks better.

I don't see any problem in my test, will send a formal patch, let me add
Signed-off-by of you if you don't mind. :)

Thanks,

> 
>>>
>>>
>>>
>>>>>
>>>>>
>>>>>>>
>>>>>>> Signed-off-by: wangzijie <wangzijie1@honor.com>
>>>>>>> ---
>>>>>>>  fs/f2fs/extent_cache.c | 1 +
>>>>>>>  1 file changed, 1 insertion(+)
>>>>>>>
>>>>>>> diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c
>>>>>>> index 199c1e7a8..6ed6f3d1d 100644
>>>>>>> --- a/fs/f2fs/extent_cache.c
>>>>>>> +++ b/fs/f2fs/extent_cache.c
>>>>>>> @@ -605,6 +605,7 @@ static struct extent_node *__insert_extent_tree(struct f2fs_sb_info *sbi,
>>>>>>>  			leftmost = false;
>>>>>>>  		} else {
>>>>>>>  			f2fs_bug_on(sbi, 1);
>>>>>>> +			return NULL;
>>>>>>>  		}
>>>>>>>  	}
>>>>>>>  
>>>>>>> -- 
>>>>>>> 2.25.1
>>>
>