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

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Message-ID: <20250916082636.237935-1-wangzijie1@honor.com>
Date: Tue, 16 Sep 2025 16:26:36 +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 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@...nel.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@...nel.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;
	}

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