Re: [PATCH resend] NFS: Don't disconnect open-owner on NFS4ERR_BAD_SEQID

[Olga Kornievskaia <aglo@umich.edu>]

On Tue, Mar 21, 2017 at 12:43 PM, Olga Kornievskaia <aglo@umich.edu> wrote:
> On Mon, Mar 20, 2017 at 7:26 PM, NeilBrown <neilb@suse.com> wrote:
>> On Mon, Mar 20 2017, Olga Kornievskaia wrote:
>>
>>> Since open_owner is no longer removed then the resources are not
>>> freed. They will not be freed until unmount  (or reboot recovery).
>>
>> I don't follow your reasoning.
>> When the last uses for a state owner is dropped by
>> nfs4_put_state_owner() (e.g. when the last open file using it is
>> closed), nfs4_put_state_owner() will add the state to
>> server->state_owners_lru.
>>
>> nfs4_gc_state_owners() is called periodically (every time any file is
>> opened I think) and it will call nfs4_remove_state_owner_locked()
>> on any state which is sufficiently old enough (hasn't been used in
>> 'lease-time'), and will then call nfs4_free_state_owner().
>> These two will release all resources.
>>
>> Does that explanation fit with your understanding?
>
> Thanks for the explanation. I was thinking about the rb-tree nodes.
> The new open finds the same rb-tree node. I incorrectly thought that
> it'd be generating a new node each time for the new open owner.

I have another question about this patch. With this patch, when the
new open owner is sent, it is sent with a seqid of what the old open
owner had. Is this intentional or accidental?

>
> Thanks.
>
>>
>> Thanks,
>> NeilBrown
>>
>>
>>>
>>> There are (buggy) servers out there that might be forcing the client
>>> to keep creating new open_owners. So if they are no longer released,
>>> can't the client get into trouble here?
>>>
>>> On Sun, Dec 18, 2016 at 7:48 PM, NeilBrown <neilb@suse.com> wrote:
>>>>
>>>> When an NFS4ERR_BAD_SEQID is received the open-owner is removed from
>>>> the ->state_owners rbtree so that it will no longer be used.
>>>>
>>>> If any stateids attached to this open-owner are still in use, and if a
>>>> request using one gets an NFS4ERR_BAD_STATEID reply, this can for bad.
>>>>
>>>> The state is marked as needing recovery and the nfs4_state_manager()
>>>> is scheduled to clean up.  nfs4_state_manager() finds states to be
>>>> recovered by walking the state_owners rbtree.  As the open-owner is
>>>> not in the rbtree, the bad state is not found so nfs4_state_manager()
>>>> completes having done nothing.  The request is then retried, with a
>>>> predicatable result (indefinite retries).
>>>>
>>>> If the stateid is for a delegation, this open_owner will be used
>>>> to open files when the delegation is returned.  For that to work,
>>>> a new open-owner needs to be presented to the server.
>>>>
>>>> This patch changes NFS4ERR_BAD_SEQID handling to leave the open-owner
>>>> in the rbtree but updates the 'create_time' so it looks like a new
>>>> open-owner.  With this the indefinite retries no longer happen.
>>>>
>>>> Signed-off-by: NeilBrown <neilb@suse.com>
>>>> ---
>>>>
>>>> Hi Trond,
>>>>  It appears this one got lost too.
>>>>  I've added a comment as I thought an explanation was needed, and
>>>>  renamed the function from "drop" to "reset".
>>>>
>>>> Thanks,
>>>> NeilBrown
>>>>
>>>>  fs/nfs/nfs4state.c | 29 +++++++++++++----------------
>>>>  1 file changed, 13 insertions(+), 16 deletions(-)
>>>>
>>>> diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
>>>> index cf869802ff23..1d152f4470cd 100644
>>>> --- a/fs/nfs/nfs4state.c
>>>> +++ b/fs/nfs/nfs4state.c
>>>> @@ -494,21 +494,18 @@ nfs4_alloc_state_owner(struct nfs_server *server,
>>>>  }
>>>>
>>>>  static void
>>>> -nfs4_drop_state_owner(struct nfs4_state_owner *sp)
>>>> -{
>>>> -       struct rb_node *rb_node = &sp->so_server_node;
>>>> -
>>>> -       if (!RB_EMPTY_NODE(rb_node)) {
>>>> -               struct nfs_server *server = sp->so_server;
>>>> -               struct nfs_client *clp = server->nfs_client;
>>>> -
>>>> -               spin_lock(&clp->cl_lock);
>>>> -               if (!RB_EMPTY_NODE(rb_node)) {
>>>> -                       rb_erase(rb_node, &server->state_owners);
>>>> -                       RB_CLEAR_NODE(rb_node);
>>>> -               }
>>>> -               spin_unlock(&clp->cl_lock);
>>>> -       }
>>>> +nfs4_reset_state_owner(struct nfs4_state_owner *sp)
>>>> +{
>>>> +       /* This state_owner is no longer usable, but must
>>>> +        * remain in place so that state recovery can find it
>>>> +        * and the opens associated with it.
>>>> +        * It may also be used for new 'open' request to
>>>> +        * return a delegation to the server.
>>>> +        * So update the 'create_time' so that it looks like
>>>> +        * a new state_owner.  This will cause the server to
>>>> +        * request an OPEN_CONFIRM to start a new sequence.
>>>> +        */
>>>> +       sp->so_seqid.create_time = ktime_get();
>>>>  }
>>>>
>>>>  static void nfs4_free_state_owner(struct nfs4_state_owner *sp)
>>>> @@ -1113,7 +1110,7 @@ void nfs_increment_open_seqid(int status, struct nfs_seqid *seqid)
>>>>
>>>>         sp = container_of(seqid->sequence, struct nfs4_state_owner, so_seqid);
>>>>         if (status == -NFS4ERR_BAD_SEQID)
>>>> -               nfs4_drop_state_owner(sp);
>>>> +               nfs4_reset_state_owner(sp);
>>>>         if (!nfs4_has_session(sp->so_server->nfs_client))
>>>>                 nfs_increment_seqid(status, seqid);
>>>>  }
>>>> --
>>>> 2.11.0
>>>>