linux-ext4 - Re: [PATCH 2/2] ext4: correct the judgment of BUG in ext4_mb_normalize

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Date:   Tue, 24 May 2022 14:09:35 +0800
From:   Baokun Li <libaokun1@...wei.com>
To:     Ritesh Harjani <ritesh.list@...il.com>
CC:     <linux-ext4@...r.kernel.org>, <tytso@....edu>,
        <adilger.kernel@...ger.ca>, <jack@...e.cz>,
        <linux-kernel@...r.kernel.org>, <yi.zhang@...wei.com>,
        <yebin10@...wei.com>, <yukuai3@...wei.com>
Subject: Re: [PATCH 2/2] ext4: correct the judgment of BUG in
 ext4_mb_normalize_request

在 2022/5/24 4:08, Ritesh Harjani 写道:
> On 22/05/21 09:42PM, Baokun Li wrote:
>> When either of the "start + size <= ac->ac_o_ex.fe_logical" or
>> "start > ac->ac_o_ex.fe_logical" conditions is met, it indicates
>> that the fe_logical is not in the allocated range.
> Sounds about right to me based on the logic in ext4_mb_use_inode_pa().
> We try to allocate/preallocate such that ac->ac_o_ex.fe_logical should fall
> within the preallocated range. So if our start or start + size doesn't include
> fe_logical then it is a bug in the ext4_mb_normalize_request() logic.
Yes, exactly.
> But should we be so harsh to hit a bug_on() or make it warn_on()?
I don't think hit a bug_on() is a problem. BUG_ON is not triggered here 
and will be triggered later.
> Also did you run any fs tests with this change.
Yes, I ran xfstests on ext3 and ext4 and found no problems.
> Since it looks like this
> logic existed since mballoc was introduced.
>
Yes, on our coverage report, those lines of code never seem to get there.

>> In this case, it should be bug_ON.
>>
>> Fixes: dfe076c106f6 ("ext4: get rid of code duplication")
> No, there is no issue with this patch. It correctly just removes the duplicate
> logic.
Okay, I'm going to remove this tag.
>> Signed-off-by: Baokun Li<libaokun1@...wei.com>
>> ---
>>   fs/ext4/mballoc.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
>> index 32410b79b664..d0fb57970648 100644
>> --- a/fs/ext4/mballoc.c
>> +++ b/fs/ext4/mballoc.c
>> @@ -4190,7 +4190,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
>>   	}
>>   	rcu_read_unlock();
>>
>> -	if (start + size <= ac->ac_o_ex.fe_logical &&
>> +	if (start + size <= ac->ac_o_ex.fe_logical ||
>>   			start > ac->ac_o_ex.fe_logical) {
>>   		ext4_msg(ac->ac_sb, KERN_ERR,
>>   			 "start %lu, size %lu, fe_logical %lu",
>> --
>> 2.31.1
>>
> .

-- 
With Best Regards,
Baokun Li