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

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Message-ID: <20190912100610.GA14773@quack2.suse.cz>
Date:   Thu, 12 Sep 2019 12:06:10 +0200
From:   Jan Kara <jack@...e.cz>
To:     Chao Yu <yuchao0@...wei.com>
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 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
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
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR