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From:   Olga Kornievskaia <aglo@umich.edu>
Date:   Mon, 11 Mar 2019 11:07:21 -0400
Message-ID: <CAN-5tyH8hFmEsAKDMDL4uey0MXh9+kY43=LEpgjj711eVUubAA@mail.gmail.com>
Subject: Re: [bug report] task hang while testing xfstests generic/323
To:     Trond Myklebust <trondmy@hammerspace.com>
Cc:     "bfields@fieldses.org" <bfields@fieldses.org>,
        "jiufei.xue@linux.alibaba.com" <jiufei.xue@linux.alibaba.com>,
        "Anna.Schumaker@netapp.com" <Anna.Schumaker@netapp.com>,
        "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
        "joseph.qi@linux.alibaba.com" <joseph.qi@linux.alibaba.com>
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Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk

On Mon, Mar 11, 2019 at 10:30 AM Trond Myklebust
<trondmy@hammerspace.com> wrote:
>
> Hi Olga,
>
> On Sun, 2019-03-10 at 18:20 -0400, Olga Kornievskaia wrote:
> > There are a bunch of cases where multiple operations are using the
> > same seqid and slot.
> >
> > Example of such weirdness is (nfs.seqid == 0x000002f4) && (nfs.slotid
> > == 0) and the one leading to the hang.
> >
> > In frame 415870, there is an OPEN using that seqid and slot for the
> > first time (but this slot will be re-used a bunch of times before it
> > gets a reply in frame 415908 with the open stateid seq=40).  (also in
> > this packet there is an example of reuse slot=1+seqid=0x000128f7 by
> > both TEST_STATEID and OPEN but let's set that aside).
> >
> > In frame 415874 (in the same packet), client sends 5 opens on the
> > SAME
> > seqid and slot (all have distinct xids). In a ways that's end up
> > being
> > alright since opens are for the same file and thus reply out of the
> > cache and the reply is ERR_DELAY. But in frame 415876, client sends
> > again uses the same seqid and slot  and in this case it's used by
> > 3opens and a test_stateid.
> >
> > Client in all this mess never processes the open stateid seq=40 and
> > keeps on resending CLOSE with seq=37 (also to note client "missed"
> > processing seqid=38 and 39 as well. 39 probably because it was a
> > reply
> > on the same kind of "Reused" slot=1 and seq=0x000128f7. I haven't
> > tracked 38 but i'm assuming it's the same). I don't know how many
> > times but after 5mins, I see a TEST_STATEID that again uses the same
> > seqid+slot (which gets a reply from the cache matching OPEN). Also
> > open + close (still with seq=37) open is replied to but after this
> > client goes into a soft lockup logs have
> > "nfs4_schedule_state_manager:
> > kthread_ruan: -4" over and over again . then a soft lockup.
> >
> > Looking back on slot 0. nfs.seqid=0x000002f3 was used in frame=415866
> > by the TEST_STATEID. This is replied to in frame 415877 (with an
> > ERR_DELAY). But before the client got a reply, it used the slot and
> > the seq by frame 415874. TEST_STATEID is a synchronous and
> > interruptible operation. I'm suspecting that somehow it was
> > interrupted and that's who the slot was able to be re-used by the
> > frame 415874. But how the several opens were able to get the same
> > slot
> > I don't know..
>
> Is this still true with the current linux-next? I would expect this
> patch
> http://git.linux-nfs.org/?p=trondmy/linux-nfs.git;a=commitdiff;h=3453d5708b33efe76f40eca1c0ed60923094b971
> to change the Linux client behaviour in the above regard.

Yes. I reproduced it against your origin/testing (5.0.0-rc7+) commit
0d1bf3407c4ae88 ("SUNRPC: allow dynamic allocation of back channel
slots").


>
> Cheers
>   Trond
>
> --
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@hammerspace.com
>
>