Return-Path: linux-nfs-owner@vger.kernel.org Received: from mail-ie0-f176.google.com ([209.85.223.176]:53721 "EHLO mail-ie0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752093AbaLDUtn (ORCPT ); Thu, 4 Dec 2014 15:49:43 -0500 Received: by mail-ie0-f176.google.com with SMTP id tr6so16004423ieb.7 for ; Thu, 04 Dec 2014 12:49:42 -0800 (PST) MIME-Version: 1.0 In-Reply-To: References: Date: Thu, 4 Dec 2014 15:49:42 -0500 Message-ID: Subject: Re: not picking a delegation stateid for IO when delegation stateid is being returned From: Olga Kornievskaia To: Trond Myklebust Cc: Linux NFS Mailing List Content-Type: text/plain; charset=UTF-8 Sender: linux-nfs-owner@vger.kernel.org List-ID: On Thu, Dec 4, 2014 at 2:08 PM, Trond Myklebust wrote: > On Thu, Dec 4, 2014 at 1:58 PM, Olga Kornievskaia wrote: >> On Thu, Dec 4, 2014 at 1:23 PM, Trond Myklebust >> wrote: >>> On Thu, Dec 4, 2014 at 12:36 PM, Olga Kornievskaia wrote: >>>> On Wed, Dec 3, 2014 at 6:50 PM, Olga Kornievskaia wrote: >>>>> On Wed, Dec 3, 2014 at 6:34 PM, Trond Myklebust >>>>> wrote: >>>>>> >>>>>> On Dec 3, 2014 6:21 PM, "Olga Kornievskaia" wrote: >>>>>>> >>>>>>> On Wed, Dec 3, 2014 at 6:13 PM, Trond Myklebust >>>>>>> wrote: >>>>>>> > On Wed, Dec 3, 2014 at 5:59 PM, Olga Kornievskaia >>>>>>> > wrote: >>>>>>> >> On Wed, Dec 3, 2014 at 3:59 PM, Trond Myklebust >>>>>>> >> wrote: >>>>>>> >>> Hi Olga, >>>>>>> >>> >>>>>>> >>> On Wed, Dec 3, 2014 at 2:54 PM, Olga Kornievskaia >>>>>>> >>> 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? > > I don't understand why the lock would already be marked as lost. > Remember that we're calling from inside nfs4_write_done() and before > calling nfs4_async_handle_error(). Sigh. I'm so confused... On November 30th I posted "is receiving BAD_STATEID during IO on delegated stateid unrecoverable?" and you've agreed that it would lead to the EIO. There are a couple of cases i'm juggling and I'm just getting confused if they are different or same. 1 is using delegation stateid for the IO while we are returning the stateid and thus getting BAD_STATEID. 2 is getting a BAD_STATEID on a delegated stateid on IO in without a deleg_return. It seems like 2nd case can also lead to the EIO. I have lossy traces from QA so it's possible that it's the 1st case and known to get the EIO. > > -- > Trond Myklebust > > Linux NFS client maintainer, PrimaryData > > trond.myklebust@primarydata.com