Received-SPF: pass (google.com: domain of linux-nfs-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Content-Type: text/plain;
        charset=us-ascii
Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.120.23.2.1\))
Subject: Re: [PATCH] NFSv4: fix stateid refreshing when CLOSE racing with OPEN
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <B6AA10F3-072D-4BFD-9D96-275EC1A9D990@redhat.com>
Date:   Fri, 4 Sep 2020 10:14:00 -0400
Cc:     Murphy Zhou <jencce.kernel@gmail.com>,
        Trond Myklebust <trondmy@hammerspace.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Content-Transfer-Encoding: quoted-printable
Message-Id: <BE205FBB-E5BC-40B2-8F3D-B7B6A7EBEB53@oracle.com>
References: <20191010074020.o2uwtuyegtmfdlze@XZHOUW.usersys.redhat.com>
 <f81d80f09c59d78c32fddd535b5604bc05c2a2b5.camel@hammerspace.com>
 <20191011084910.joa3ptovudasyo7u@xzhoux.usersys.redhat.com>
 <cbe6a84f9cd61a8f60e70c05a07b3247030a262f.camel@hammerspace.com>
 <6AAFBD30-1931-49A8-8120-B7171B0DA01C@redhat.com>
 <20200904030411.enioqeng4wxftucd@xzhoux.usersys.redhat.com>
 <B6AA10F3-072D-4BFD-9D96-275EC1A9D990@redhat.com>
To:     Benjamin Coddington <bcodding@redhat.com>
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk


> On Sep 4, 2020, at 6:55 AM, Benjamin Coddington <bcodding@redhat.com> =
wrote:
>=20
> On 3 Sep 2020, at 23:04, Murphy Zhou wrote:
>=20
>> Hi Benjamin,
>>=20
>> On Thu, Sep 03, 2020 at 01:54:26PM -0400, Benjamin Coddington wrote:
>>>=20
>>> On 11 Oct 2019, at 10:14, Trond Myklebust wrote:
>>>> On Fri, 2019-10-11 at 16:49 +0800, Murphy Zhou wrote:
>>>>> On Thu, Oct 10, 2019 at 02:46:40PM +0000, Trond Myklebust wrote:
>>>>>> On Thu, 2019-10-10 at 15:40 +0800, Murphy Zhou wrote:
>>> ...
>>>>>>> @@ -3367,14 +3368,16 @@ static bool
>>>>>>> nfs4_refresh_open_old_stateid(nfs4_stateid *dst,
>>>>>>> 			break;
>>>>>>> 		}
>>>>>>> 		seqid_open =3D state->open_stateid.seqid;
>>>>>>> -		if (read_seqretry(&state->seqlock, seq))
>>>>>>> -			continue;
>>>>>>>=20
>>>>>>> 		dst_seqid =3D be32_to_cpu(dst->seqid);
>>>>>>> -		if ((s32)(dst_seqid - be32_to_cpu(seqid_open)) =
>=3D 0)
>>>>>>> +		if ((s32)(dst_seqid - be32_to_cpu(seqid_open)) > =
0)
>>>>>>> 			dst->seqid =3D cpu_to_be32(dst_seqid + =
1);
>>>>>>=20
>>>>>> This negates the whole intention of the patch you reference in =
the
>>>>>> 'Fixes:', which was to allow us to CLOSE files even if seqid =
bumps
>>>>>> have
>>>>>> been lost due to interrupted RPC calls e.g. when using 'soft' or
>>>>>> 'softerr' mounts.
>>>>>> With the above change, the check could just be tossed out
>>>>>> altogether,
>>>>>> because dst_seqid will never become larger than seqid_open.
>>>>>=20
>>>>> Hmm.. I got it wrong. Thanks for the explanation.
>>>>=20
>>>> So to be clear: I'm not saying that what you describe is not a =
problem.
>>>> I'm just saying that the fix you propose is really no better than
>>>> reverting the entire patch. I'd prefer not to do that, and would =
rather
>>>> see us look for ways to fix both problems, but if we can't find =
such as
>>>> fix then that would be the better solution.
>>>=20
>>> Hi Trond and Murphy Zhou,
>>>=20
>>> Sorry to resurrect this old thread, but I'm wondering if any =
progress was
>>> made on this front.
>>=20
>> This failure stoped showing up since v5.6-rc1 release cycle
>> in my records. Can you reproduce this on latest upstream kernel?
>=20
> I'm seeing it on generic/168 on a v5.8 client against a v5.3 knfsd =
server.
> When I test against v5.8 server, the test takes longer to complete and =
I
> have yet to reproduce the livelock.
>=20
> - on v5.3 server takes ~50 iterations to produce, each test completes =
in ~40
> seconds
> - on v5.8 server my test has run ~750 iterations without getting into
> the lock, each test takes ~60 seconds.
>=20
> I suspect recent changes to the server have changed the timing of open
> replies such that the problem isn't reproduced on the client.

The Linux NFS server in v5.4 does behave differently than earlier
kernels with NFSv4.0, and it is performance-related. The filecache
went into v5.4, and that seems to change the frequency at which
the server offers delegations.

I'm looking into it, and learning a bunch.


--
Chuck Lever