Re: [PATCH] btrfs: add delayed_iput list head to btrfs inode

[Eric Sandeen <esandeen@redhat.com>]

On Feb 5, 2013, at 8:11 PM, Liu Bo <bo.li.liu@oracle.com> wrote:

> On Tue, Feb 05, 2013 at 03:14:05PM -0800, Zach Brown wrote:
>>> +    struct btrfs_inode *b_inode = BTRFS_I(inode);
>>> +    struct btrfs_fs_info *fs_info = b_inode->root->fs_info;
>>> 
>>>    if (atomic_add_unless(&inode->i_count, -1, 1))
>>>        return;
>>> 
>>> -    delayed = kmalloc(sizeof(*delayed), GFP_NOFS | __GFP_NOFAIL);
>>> -    delayed->inode = inode;
>>> -
>>>    spin_lock(&fs_info->delayed_iput_lock);
>>> -    list_add_tail(&delayed->list, &fs_info->delayed_iputs);
>>> +    list_add_tail(&b_inode->delayed_iput, &fs_info->delayed_iputs);
>>>    spin_unlock(&fs_info->delayed_iput_lock);
>>> }
>> 
>> Hmm.  I'm not great with inode life cycles, but isn't this only safe if
>> someone else can't get an i_count reference while this is in flight?  It
>> looks like the final iput does the unhashing, and so on, so couldn't an
>> iget/iput race with this and try to add the inode's list_head twice?
> 
> Yeah, same concern here.  Basically this will result in inodes still being
> in use on unmount.
> 
> Actually I did a similar one, here is some disscussion:
> 
> https://patchwork.kernel.org/patch/1824711/
> 
Ok, thanks all.  We should remove Jeff's comment then, it sure sounded like a good idea...

Eric

> thanks,
> liubo
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