linux-kernel - Re: [f2fs-dev] [PATCH v2 2/2] f2fs: fix infinite loop in __insert_extent

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Message-ID: <20250916070946.231825-1-wangzijie1@honor.com>
Date: Tue, 16 Sep 2025 15:09:46 +0800
From: wangzijie <wangzijie1@...or.com>
To: <chao@...nel.org>
CC: <bintian.wang@...or.com>, <feng.han@...or.com>, <jaegeuk@...nel.org>,
	<linux-f2fs-devel@...ts.sourceforge.net>, <linux-kernel@...r.kernel.org>,
	<wangzijie1@...or.com>
Subject: Re: [f2fs-dev] [PATCH v2 2/2] f2fs: fix infinite loop in __insert_extent_tree()

>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".



>> 
>> 
>>>>
>>>> Signed-off-by: wangzijie <wangzijie1@...or.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