Re: V4 unmount causes a GETATTR

[Steve Dickson <SteveD@redhat.com>]

On 16/02/13 00:17, Myklebust, Trond wrote:
>> -----Original Message-----
>> From: linux-nfs-owner@vger.kernel.org [mailto:linux-nfs-
>> owner@vger.kernel.org] On Behalf Of Steve Dickson
>> Sent: Friday, February 15, 2013 4:46 PM
>> To: J. Bruce Fields
>> Cc: linux-nfs@vger.kernel.org
>> Subject: Re: V4 unmount causes a GETATTR
>>
>>
>>
>> On 15/02/13 13:25, J. Bruce Fields wrote:
>>> On Fri, Feb 15, 2013 at 10:46:00AM -0500, Steve Dickson wrote:
>>>> Hello,
>>>>
>>>> I have not tracked down as to the exact reason, but it appears umount
>>>> of v4 file system cause the directory to be revalidating causing the
>>>> GETATTR.
>>>>
>>>> Is this revalidation really necessary on an unmount?
>>>
>>> I don't know, maybe not.  But even if it's not, there are other things
>>> (like cleaning up state) that the client will likely try to do on
>>> unmount.  In the presence of delegations it could have dirty data that
>>> it's required to write back even if applications don't currently hold
>>> any open files.
>> Understood with dirty data... but what I as seeing was a v4 mount and then a
>> reboot with no activity on the mount point...
>>
>>>
>>> So I don't think we can promise umount will work without the network.
>> Again with open files (aka activity on the mount point) I agree but with no
>> activity or open files, I'm think that GETATTR is simply not necessary...
> 
> You'd need to add a lookup intent specifically for umount. Otherwise the filesystem will not be able distinguish between path lookups for umount and other activity.
> 
> Also note that "no activity or open files" is no guarantee that you won't be holding delegations or pNFS layouts to return; you may still see hangs.
> 
I've also noticed force mounts this clean up does not happen (aka the GETATTR is not sent)... which is the price of doing forced mounts... 

steved.