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.
--
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@xxxxxxxxxxxxxxx
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