From: Scott Mayhew <smayhew@redhat.com>
To: Trond Myklebust <trondmy@hammerspace.com>
Cc: "bfields@fieldses.org" <bfields@fieldses.org>,
"linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
"jlayton@kernel.org" <jlayton@kernel.org>
Subject: Re: [PATCH] nfsd: CB_RECALL can race with FREE_STATEID
Date: Tue, 30 Apr 2019 14:46:14 -0400 [thread overview]
Message-ID: <20190430184614.GF15226@coeurl.usersys.redhat.com> (raw)
In-Reply-To: <15806b00f7ba569a109549eb551bb116d981226d.camel@hammerspace.com>
On Thu, 18 Apr 2019, Trond Myklebust wrote:
> On Thu, 2019-04-18 at 16:50 -0400, Scott Mayhew wrote:
> > On Thu, 18 Apr 2019, J. Bruce Fields wrote:
> >
> > > On Thu, Apr 18, 2019 at 09:24:00AM -0400, Scott Mayhew wrote:
> > > > While trying to track down some issues involving large numbers of
> > > > delegations being recalled/revoked, I caught the server setting
> > > > SEQ4_STATUS_CB_PATH_DOWN while the client was actively responding
> > > > to
> > > > CB_RECALLs. It turns out that the client had already done a
> > > > TEST_STATEID and FREE_STATEID for a delegation being recalled by
> > > > the
> > > > time it received the CB_RECALL.
> > >
> > > That's interesting, thanks!
> > >
> > > This exception seems awfully narrow, though.
> > >
> > > If we get back any NFS-level error at all, then I think the
> > > callback
> > > channel is working (am I wrong?)
> >
> > Correct, if the client replies with either NFS4ERR_DELAY or
> > NFS4ERR_BAD_STATEID, the server will retry 1 time (see dl_retries).
> > After that, we fall thru and nfsd4_cb_recall_done() returns -1 which
> > causes the SEQ4_STATUS_CB_PATH_DOWN flag to be set.
>
> There is no handling of NFS4ERR_DELAY in nfsd4_cb_recall_done().
>
> As far as I can see, therefore, if the client returns NFS4ERR_DELAY
> (which it usually does if it is already in the process of returning the
> delegation) then the recall will fail immediately.
You're right, I had NFS4ERR_DELAY on the brain because I was seeing
those periodically in conjunction with the BIND_CONN_TO_SESSION calls
that were occurring while handling the bogus CB_PATH_DOWN flags from the
server.
-Scott
>
> > > and telling the client to set up a new
> > > one is probably not going to help. The best we can do is probably
> > > just
> > > give up
> >
> > That's what the patch is essentially doing. Or are you saying don't
> > even bother with the checks but still return 1 so we don't set the
> > SEQ4_STATUS_CB_PATH_DOWN flag?
> >
> > > and let the client deal with the ensuing
> > > RECALLABLE_STATE_REVOKED flag.
> >
> > The client's already dealing with the RECALLABLE_STATE_REVOKED flag,
> > that's why it sent a TEST_STATEID and FREE_STATEID before it got this
> > particular CB_RECALL. The idea behind the patch is to not give the
> > state manager on the client additional work by setting CB_PATH_DOWN
> > when
> > the callback channel is clearly working...
> >
>
> Either way, the Linux client will ignore any further sequence flags
> until it is done with the recovery of the RECALLABLE_STATE_REVOKED
> flag. The reason is that the flags are edge triggered (i.e. they don't
> clear until the state changes), and so we need to be able to perform a
> full recovery before we can check them again.
>
> --
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@hammerspace.com
>
>
prev parent reply other threads:[~2019-04-30 18:46 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-18 13:24 [PATCH] nfsd: CB_RECALL can race with FREE_STATEID Scott Mayhew
2019-04-18 15:13 ` J. Bruce Fields
2019-04-18 20:50 ` Scott Mayhew
2019-04-18 21:37 ` J. Bruce Fields
2019-04-30 18:58 ` Scott Mayhew
2019-04-30 19:03 ` Trond Myklebust
2019-05-02 11:35 ` Scott Mayhew
2019-05-02 11:49 ` Trond Myklebust
2019-04-18 22:03 ` Trond Myklebust
2019-04-18 23:42 ` bfields
2019-04-30 18:46 ` Scott Mayhew [this message]
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