> On Apr 28, 2016, at 11:56 AM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote:
>
> Chuck or Anna,
>
> If the patch is accepted, do you mind expanding the commit message to
> include the wording about the LOCK and CB_RECALL race (so that it's
> documented to look back into it).
Anna's choice.
> On Thu, Apr 28, 2016 at 10:09 AM, Anna Schumaker
> <Anna.Schumaker@xxxxxxxxxx> wrote:
>> On 04/28/2016 10:06 AM, Chuck Lever wrote:
>>>
>>>> On Apr 28, 2016, at 9:13 AM, Anna Schumaker <Anna.Schumaker@xxxxxxxxxx> wrote:
>>>>
>>>> The patch looks pretty straightforward to me, and it sounds like it fixes a few problems that people are seeing. One question (below):
>>>>
>>>> On 04/28/2016 08:43 AM, William Dauchy wrote:
>>>>> Hello Anna,
>>>>>
>>>>> Could you have a look at this one please?
>>>>>
>>>>> Thanks,
>>>>>
>>>>> William
>>>>>
>>>>> On Tue, Apr 26, 2016 at 4:24 PM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote:
>>>>>> I believe this patch also helps with a race between a LOCK and
>>>>>> CB_RECALL. Application does a lock as the delegation is being
>>>>>> recalled. The lock thread sees the delegated state and acquires a
>>>>>> local lock. At the same time delegation doesn't see it the lock yet
>>>>>> and returns the delegation. Application proceeds to do IO. It ends up
>>>>>> using an open stateid for the IO (as there is no delegation stateid or
>>>>>> lock stateid). The server is unaware of the lock so it can give that
>>>>>> lock to somebody else. Yet this client thinks it has a local lock. It
>>>>>> leads to inconsistent data between clients.
>>>>>>
>>>>>> On Mon, Apr 11, 2016 at 4:20 PM, Chuck Lever <chuck.lever@xxxxxxxxxx> 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@xxxxxxxxxx>
>>>>>>> ---
>>>>>>> Hi-
>>>>>>>
>>>>>>> This fix appears to be both safe and effective. Please consider
>>>>>>> it for v4.7 and for stable. Thanks!
>>>>>>>
>>>>>>>
>>>>>>> fs/nfs/nfs4proc.c | 4 ++++
>>>>>>> 1 file changed, 4 insertions(+)
>>>>>>>
>>>>>>> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
>>>>>>> index 01bef06..c40f1b6 100644
>>>>>>> --- a/fs/nfs/nfs4proc.c
>>>>>>> +++ b/fs/nfs/nfs4proc.c
>>>>>>> @@ -6054,6 +6054,7 @@ static int nfs41_lock_expired(struct nfs4_state *state, struct file_lock *reques
>>>>>>> static int _nfs4_proc_setlk(struct nfs4_state *state, int cmd, struct file_lock *request)
>>>>>>> {
>>>>>>> struct nfs_inode *nfsi = NFS_I(state->inode);
>>>>>>> + struct nfs4_state_owner *sp = state->owner;
>>>>>>> unsigned char fl_flags = request->fl_flags;
>>>>>>> int status = -ENOLCK;
>>>>>>>
>>>>>>> @@ -6068,6 +6069,7 @@ static int _nfs4_proc_setlk(struct nfs4_state *state, int cmd, struct file_lock
>>>>>>> status = do_vfs_lock(state->inode, request);
>>>>>>> if (status < 0)
>>>>>>> goto out;
>>>>>>> + mutex_lock(&sp->so_delegreturn_mutex);
>>>>
>>>> From what I can tell, the first call to do_vfs_lock() in this function is used to test if we can take the lock locally. Do we need to worry about this racing with delegreturn, too?
>>>
>>> When I included that call in the critical section,
>>> cthon04 locking tests deadlocked.
>>
>> Got it. Thanks for checking!
>>
>> Anna
>>
>>>
>>>
>>>> Thanks,
>>>> Anna
>>>>
>>>>>>> down_read(&nfsi->rwsem);
>>>>>>> if (test_bit(NFS_DELEGATED_STATE, &state->flags)) {
>>>>>>> /* Yes: cache locks! */
>>>>>>> @@ -6075,9 +6077,11 @@ static int _nfs4_proc_setlk(struct nfs4_state *state, int cmd, struct file_lock
>>>>>>> request->fl_flags = fl_flags & ~FL_SLEEP;
>>>>>>> status = do_vfs_lock(state->inode, request);
>>>>>>> up_read(&nfsi->rwsem);
>>>>>>> + mutex_unlock(&sp->so_delegreturn_mutex);
>>>>>>> goto out;
>>>>>>> }
>>>>>>> up_read(&nfsi->rwsem);
>>>>>>> + mutex_unlock(&sp->so_delegreturn_mutex);
>>>>>>> status = _nfs4_do_setlk(state, cmd, request, NFS_LOCK_NEW);
>>>>>>> out:
>>>>>>> request->fl_flags = fl_flags;
>>>
>>> --
>>> Chuck Lever
>>>
>>>
>>>
>>
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