linux-kernel - Re: [PATCH] hugetlbfs: make BUG_ON(!inode) takes effect in hugetlbfs

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Date:   Mon, 18 Jan 2021 16:48:37 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Muchun Song <smuchun@...il.com>
CC:     <mike.kravetz@...cle.com>, <linux-mm@...ck.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] hugetlbfs: make BUG_ON(!inode) takes effect in
 hugetlbfs_setattr

Hi:

On 2021/1/18 15:59, Muchun Song wrote:
> On Sat, Jan 16, 2021 at 5:11 PM Miaohe Lin <linmiaohe@...wei.com> wrote:
>>
>> When we reach here with inode = NULL, we should have crashed as inode has
>> already been dereferenced via hstate_inode. In order to make BUG_ON(!inode)
>> takes effect, we should defer initializing hstate until we really need it.
>> Also do this for hugetlbfs_inode_info as it's only used when ia_valid is
>> verified with ATTR_SIZE.
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
>> ---
>>  fs/hugetlbfs/inode.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
>> index 740693d7f255..9b221b87fbea 100644
>> --- a/fs/hugetlbfs/inode.c
>> +++ b/fs/hugetlbfs/inode.c
>> @@ -755,10 +755,8 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
>>  static int hugetlbfs_setattr(struct dentry *dentry, struct iattr *attr)
>>  {
>>         struct inode *inode = d_inode(dentry);
>> -       struct hstate *h = hstate_inode(inode);
> 
> If inode == NULL, it will panic here when we access inode->i_sb.
> I have seen many other file system implementations about setattr,
> they all think that d_inode() will return a non-NULL pointer. So
> I prefer to just remove the BUG_ON().
> 

Sounds reasonable. Will do it in v2. Many thanks.

> Thanks.
> 
> 
>>         int error;
>>         unsigned int ia_valid = attr->ia_valid;
>> -       struct hugetlbfs_inode_info *info = HUGETLBFS_I(inode);
>>
>>         BUG_ON(!inode);
>>
>> @@ -767,6 +765,8 @@ static int hugetlbfs_setattr(struct dentry *dentry, struct iattr *attr)
>>                 return error;
>>
>>         if (ia_valid & ATTR_SIZE) {
>> +               struct hstate *h = hstate_inode(inode);
>> +               struct hugetlbfs_inode_info *info = HUGETLBFS_I(inode);
>>                 loff_t oldsize = inode->i_size;
>>                 loff_t newsize = attr->ia_size;
>>
>> --
>> 2.19.1
>>
> .
>