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From:   Olga Kornievskaia <aglo@umich.edu>
Date:   Tue, 26 Sep 2023 10:31:04 -0400
Message-ID: <CAN-5tyGA46W+UTbVNn5xnzqTgdgTvT7=nwx9yo3zez4mTEo5Rg@mail.gmail.com>
Subject: Re: [PATCH 2/2] NFSv4: Fix a state manager thread deadlock regression
To:     Trond Myklebust <trondmy@hammerspace.com>
Cc:     "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
        "Anna.Schumaker@netapp.com" <Anna.Schumaker@netapp.com>,
        "neilb@suse.de" <neilb@suse.de>,
        "schumaker.anna@gmail.com" <schumaker.anna@gmail.com>
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On Fri, Sep 22, 2023 at 5:07=E2=80=AFPM Trond Myklebust <trondmy@hammerspac=
e.com> wrote:
>
> On Fri, 2023-09-22 at 17:00 -0400, Olga Kornievskaia wrote:
> > On Fri, Sep 22, 2023 at 3:05=E2=80=AFPM Trond Myklebust
> > >
> > > Oh crap... Yes, that is a bug. Can you please apply the attached
> > > patch
> > > on top of the original, and see if that fixes the problem?
> >
> > I can't consistently reproduce the problem. Out of several xfstests
> > runs a couple got stuck in that state. So when I apply that patch and
> > run, I can't tell if i'm no longer hitting or if I'm just not hitting
> > the right condition.
> >
> > Given I don't exactly know what's caused it I'm trying to find
> > something I can hit consistently. Any ideas? I mean this stack trace
> > seems to imply a recovery open but I'm not doing any server reboots
> > or
> > connection drops.
> >
> > >
>
> If I'm right about the root cause, then just turning off delegations on
> the server, setting up a NFS swap partition and then running some
> ordinary file open/close workload against the exact same server would
> probably suffice to trigger your stack trace 100% reliably.

Getting back to this now. Thanks for v2 and I'll test. But I'm still
unclear, is there a requirement that delegations have to be off for
when the client has NFS over swap enabled? I always run with
delegations on in ONTAP and run xfstests. I don't usually run with NFS
over swap enabled but sometimes I do. So what should be the
expectations? If I choose this kernel configuration, then deadlock is
possible?
>
> I'll see if I can find time to test it over the weekend.
>
> --
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@hammerspace.com
>
>