Re: [PATCH] NFS: Fix an LOCK/OPEN race when unlinking an open file

[Chuck Lever <chuck.lever@oracle.com>]

> On Apr 25, 2016, at 10:34 AM, William Dauchy <wdauchy@gmail.com> wrote:
> 
> Hello,
> 
> On Mon, Apr 11, 2016 at 10:20 PM, Chuck Lever <chuck.lever@oracle.com> wrote:
>> At Connectathon 2016, we found that recent upstream Linux clients
>> would occasionally send a LOCK operation with a zero stateid. This
>> appeared to happen in close proximity to another thread returning
>> a delegation before unlinking the same file while it remained open.
>> 
>> Earlier, the client received a write delegation on this file and
>> returned the open stateid. Now, as it is getting ready to unlink the
>> file, it returns the write delegation. But there is still an open
>> file descriptor on that file, so the client must OPEN the file
>> again before it returns the delegation.
>> 
>> Since commit 24311f884189 ('NFSv4: Recovery of recalled read
>> delegations is broken'), nfs_open_delegation_recall() clears the
>> NFS_DELEGATED_STATE flag _before_ it sends the OPEN. This allows a
>> racing LOCK on the same inode to be put on the wire before the OPEN
>> operation has returned a valid open stateid.
>> 
>> To eliminate this race, serialize delegation return with the
>> acquisition of a file lock on the same file. Adopt the same approach
>> as is used in the unlock path.
>> 
>> Fixes: 24311f884189 ('NFSv4: Recovery of recalled read ... ')
>> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> 
> 
> Is it something which is going to be merged in v4.7?
> It also might be a good candidate for stable?

William, only the NFS maintainers can answer these questions.
I really don't know.

--
Chuck Lever