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

[Chao Yu <chao@kernel.org>]

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


> 
> 
> 
>>>
>>>
>>>>>
>>>>> 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
>