On Thu, Dec 4, 2014 at 1:23 PM, Trond Myklebust
<trond.myklebust@xxxxxxxxxxxxxxx> wrote:
> On Thu, Dec 4, 2014 at 12:36 PM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote:
>> On Wed, Dec 3, 2014 at 6:50 PM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote:
>>> On Wed, Dec 3, 2014 at 6:34 PM, Trond Myklebust
>>> <trond.myklebust@xxxxxxxxxxxxxxx> wrote:
>>>>
>>>> On Dec 3, 2014 6:21 PM, "Olga Kornievskaia" <aglo@xxxxxxxxx> wrote:
>>>>>
>>>>> On Wed, Dec 3, 2014 at 6:13 PM, Trond Myklebust
>>>>> <trond.myklebust@xxxxxxxxxxxxxxx> wrote:
>>>>> > On Wed, Dec 3, 2014 at 5:59 PM, Olga Kornievskaia <aglo@xxxxxxxxx>
>>>>> > wrote:
>>>>> >> On Wed, Dec 3, 2014 at 3:59 PM, Trond Myklebust
>>>>> >> <trond.myklebust@xxxxxxxxxxxxxxx> wrote:
>>>>> >>> Hi Olga,
>>>>> >>>
>>>>> >>> On Wed, Dec 3, 2014 at 2:54 PM, Olga Kornievskaia <aglo@xxxxxxxxx>
>>>>> >>> wrote:
>>>>> >>>> Hi folks,
>>>>> >>>>
>>>>> >>>> I would like an opinion about changing code in such as way that we
>>>>> >>>> don't select a delegation stateid for an IO operation when this
>>>>> >>>> particular delegation is being returned.
>>>>> >>>>
>>>>> >>>> The reason it's some what problematic is that we send out a
>>>>> >>>> DELEG_RETURN and then we don't remove the stateid until we receive a
>>>>> >>>> reply. In the mean while, an IO operation can be happening and in
>>>>> >>>> nfs4_select_rw_stateid() it sees a delegation stateid and uses it.
>>>>> >>>> Well, at the server, it finishes processing DELEG_RETURN before
>>>>> >>>> getting an IO op and by that time the server is finished with the
>>>>> >>>> stateid and can error an IO operation with BAD_STATEID.
>>>>> >>>>
>>>>> >>>> diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
>>>>> >>>> index 7f3f606..4f6f6c9 100644
>>>>> >>>> --- a/fs/nfs/delegation.c
>>>>> >>>> +++ b/fs/nfs/delegation.c
>>>>> >>>> @@ -854,7 +854,8 @@ bool nfs4_copy_delegation_stateid(nfs4_stateid
>>>>> >>>> *dst, struct inode *in
>>>>> >>>> flags &= FMODE_READ|FMODE_WRITE;
>>>>> >>>> rcu_read_lock();
>>>>> >>>> delegation = rcu_dereference(nfsi->delegation);
>>>>> >>>> - ret = (delegation != NULL && (delegation->type & flags) ==
>>>>> >>>> flags);
>>>>> >>>> + ret = (delegation != NULL && (delegation->type & flags) ==
>>>>> >>>> flags &&
>>>>> >>>> + !test_bit(NFS_DELEGATION_RETURNING,
>>>>> >>>> &delegation->flags));
>>>>> >>>> if (ret) {
>>>>> >>>> nfs4_stateid_copy(dst, &delegation->stateid);
>>>>> >>>> nfs_mark_delegation_referenced(delegation);
>>>>> >>>
>>>>> >>> The above cannot eliminate the possibility that we won't use a
>>>>> >>> delegation while it is being returned. It will at best just reduce the
>>>>> >>> window of opportunity.
>>>>> >>>
>>>>> >>
>>>>> >> You are right this are still problems. Actually, we might set the bit
>>>>> >> but not yet get the open stateid from the open with deleg_cur and
>>>>> >> that's not good. It would be good to know we got the open stateid and
>>>>> >> then pick that.
>>>>> >>
>>>>> >>> So, why is this being considered to be a problem in the first place?
>>>>> >>> Are you seeing a measurable performance impact on a real life workload
>>>>> >>> (as opposed to some 1-in-a-billion occurrence from a QA test :-))?
>>>>> >>
>>>>> >> Unfortunately, this problem is quite common and I hit it all the time
>>>>> >> on my setup. This leads to client seizing IO on that file and
>>>>> >> returning EIO. It's an unrecoverable error. I'm trying to figure out
>>>>> >> how to eliminate getting to that state.
>>>>> >>
>>>>> >
>>>>> > It definitely isn't intended to be an irrecoverable error. The client
>>>>> > is supposed to just replay the write after updating the stateid.
>>>>>
>>>>> open(deleg_cur) call / reply
>>>>> lock() call/reply
>>>>> deleg_return() call
>>>>> write(with deluge_stateid) call gets BAD_STATEID
>>>>> state recovery code marks lock state lost -> EIO.
>>>>
>>>> Why is it marking the lock as lost? If the recovery succeeded, it should
>>>> notice that the stateid has changed and instead retry.
>>>
>>> I'll get you a better explanation tomorrow besides saying "that's what
>>> I see when I run the code".
>>
>> nfs4_async_handle_error() initiates state recovery
>> nfs4_reclaim_open_state() eventually calls nfs4_reclaim_locks() which
>> marks the lock LOST. state is delegated so the kernel logs "lock
>> reclaim failed".
>> write retries and in nfs4_copy_ lock_stateid() the lock is marked LOST
>> and the nfs4_select_rw_stateid() fails with EIO.
>>
>>>
>>>> What kernel is this?
>>>
>>> This is upstream.
>
> So why isn't nfs4_write_stateid_changed() catching the change before
> we even get to nfs4_async_handle_error()? That's where this race is
> supposed to get resolved.
Probably because nfs4_stateid_is_current() returns true because
nfs4_set_rw_stateid() calls the nfs4_select_rw_stateid() and finds the
lock lost?
>
> --
> Trond Myklebust
>
> Linux NFS client maintainer, PrimaryData
>
> trond.myklebust@xxxxxxxxxxxxxxx
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