From: "J. Bruce Fields" <bfields@fieldses.org>
To: Scott Mayhew <smayhew@redhat.com>
Cc: jlayton@kernel.org, linux-nfs@vger.kernel.org
Subject: Re: [PATCH] nfsd: CB_RECALL can race with FREE_STATEID
Date: Thu, 18 Apr 2019 17:37:30 -0400 [thread overview]
Message-ID: <20190418213730.GA1891@fieldses.org> (raw)
In-Reply-To: <20190418205024.GB15226@coeurl.usersys.redhat.com>
On Thu, Apr 18, 2019 at 04:50:24PM -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.
>
> > 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?
Right, I don't see any point returning -1 (which ends up setting
CB_PATH_DOWN) in any case where we get an nfs-level error. If the
client got so far as returning an error, then the callback path is
working.
I'm not sure exactly what errors *should* result in CB_PATH_DOWN,
though. ETIMEDOUT, ENOTCONN, EIO? And maybe we should be checking for
those in nfsd4_cb_done, and do away with the convention that -1 means
CB_PATH_DOWN. I don't think there's a reason individual callback ops
would need different rules for when to mark the callback channel down.
--b.
>
> > 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...
>
> -Scott
> >
> > --b.
> >
> > >
> > > Signed-off-by: Scott Mayhew <smayhew@redhat.com>
> > > ---
> > > fs/nfsd/nfs4state.c | 8 ++++++++
> > > 1 file changed, 8 insertions(+)
> > >
> > > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> > > index 6a45fb00c5fc..e88e429133a8 100644
> > > --- a/fs/nfsd/nfs4state.c
> > > +++ b/fs/nfsd/nfs4state.c
> > > @@ -3958,6 +3958,14 @@ static int nfsd4_cb_recall_done(struct nfsd4_callback *cb,
> > > rpc_delay(task, 2 * HZ);
> > > return 0;
> > > }
> > > + /*
> > > + * Race: client may have done a FREE_STATEID before
> > > + * receiving the CB_RECALL.
> > > + */
> > > + if (dp->dl_stid.sc_type == NFS4_REVOKED_DELEG_STID &&
> > > + refcount_read(&dp->dl_stid.sc_count) == 1 &&
> > > + list_empty(&dp->dl_recall_lru))
> > > + return 1;
> > > /*FALLTHRU*/
> > > default:
> > > return -1;
> > > --
> > > 2.17.2
next prev parent reply other threads:[~2019-04-18 21:37 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 [this message]
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
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