linux-kernel - Re: [RFC PATCH 1/3] debugfs: fix automount inode i

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Message-ID: <CACZ9PQUxZOLUjdt-t1N5mWrbWxNyfv6tsgtHCgXCeUa5Vm_ONw@mail.gmail.com>
Date:	Mon, 8 Feb 2016 11:28:52 +0100
From:	Roman Peniaev <r.peniaev@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 1/3] debugfs: fix automount inode i_nlink references

On Mon, Feb 8, 2016 at 7:38 AM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Thu, Dec 10, 2015 at 01:47:12PM +0100, Roman Pen wrote:
>> Directory inodes should start off with i_nlink == 2 (for "." entry).
>> Of course the same rule should be applied to automount dentries for
>> child and parent inodes as well.
>>
>> Also now automount dentry does fsnotify_mkdir.
>>
>> Without this patch kernel complains when sees i_nlink == 0:
>
> How can the kernel see this?  What did you do to trigger this?

Yes, sorry, I had to be more precise on this.
That happens on unlinking of automount dentry.

Easily can be reproduced:

    autom = debugfs_create_automount("automount", parentd, vfsmount_cb, data);
    BUG_ON(IS_ERR_OR_NULL(autom));
    debugfs_remove(autom);

You will immediately see one warning on attempt to drop_nlink() (which is zero)
for automount dentry.

The second warning happens when you unlink 'parentd', because
debugfs_create_automount() did not increase the nlink for parent
inode.

Do I need to resend this patch with more precise description?

--
Roman

>
> thanks,
>
> greg k-h