linux-kernel - Re: [PATCH] quota: fix wrong condition in is_quota

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Date:   Mon, 16 Sep 2019 10:53:08 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jan Kara <jack@...e.cz>
CC:     Jan Kara <jack@...e.com>, <chao@...nel.org>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] quota: fix wrong condition in is_quota_modification()

On 2019/9/12 18:06, Jan Kara wrote:
> On Wed 11-09-19 17:36:50, Chao Yu wrote:
>> Quoted from
>> commit 3da40c7b0898 ("ext4: only call ext4_truncate when size <= isize")
>>
>> " At LSF we decided that if we truncate up from isize we shouldn't trim
>>   fallocated blocks that were fallocated with KEEP_SIZE and are past the
>>  new i_size.  This patch fixes ext4 to do this. "
>>
>> And generic/092 of fstest have covered this case for long time, however
>> is_quota_modification() didn't adjust based on that rule, so that in
>> below condition, we will lose to quota block change:
>> - fallocate blocks beyond EOF
>> - remount
>> - truncate(file_path, file_size)
>>
>> Fix it.
>>
>> Signed-off-by: Chao Yu <yuchao0@...wei.com>
>> ---
>>  include/linux/quotaops.h | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/include/linux/quotaops.h b/include/linux/quotaops.h
>> index dc905a4ff8d7..bd30acad3a7f 100644
>> --- a/include/linux/quotaops.h
>> +++ b/include/linux/quotaops.h
>> @@ -22,7 +22,7 @@ static inline struct quota_info *sb_dqopt(struct super_block *sb)
>>  /* i_mutex must being held */
>>  static inline bool is_quota_modification(struct inode *inode, struct iattr *ia)
>>  {
>> -	return (ia->ia_valid & ATTR_SIZE && ia->ia_size != inode->i_size) ||
>> +	return (ia->ia_valid & ATTR_SIZE && ia->ia_size <= inode->i_size) ||
>>  		(ia->ia_valid & ATTR_UID && !uid_eq(ia->ia_uid, inode->i_uid)) ||
>>  		(ia->ia_valid & ATTR_GID && !gid_eq(ia->ia_gid, inode->i_gid));
>>  }
> 
> OK, but your change makes i_size extension not to be quota modification

I just try to adapt below rules covered with generic/092, which restrict to not
trim preallocate blocks beyond i_size, in that case, filesystem won't change
i_blocks.

1) truncate(i_size) will trim all blocks past i_size.
2) truncate(x) where x > i_size will not trim all blocks past i_size.

However, I'm okay with your change, because there could be filesystems won't
follow above rule.

Thanks,

> which is IMO wrong. So I think the condition should just be:
> 
> 	return (ia->ia_valid & ATTR_SIZE) || ...
> 
> I'll fix the patch up and pull it into my tree.
> 
> 									Honza
>