On Thu, 2016-11-17 at 16:53 -0500, Olga Kornievskaia wrote:
> On Thu, Nov 17, 2016 at 4:45 PM, Trond Myklebust
> <trondmy@xxxxxxxxxxxxxxx> wrote:
> >
> > On Thu, 2016-11-17 at 16:26 -0500, bfields@xxxxxxxxxxxx wrote:
> > >
> > > On Thu, Nov 17, 2016 at 04:05:32PM -0500, Olga Kornievskaia
> > > wrote:
> > > >
> > > >
> > > > On Thu, Nov 17, 2016 at 3:46 PM, bfields@xxxxxxxxxxxx
> > > > <bfields@xxxxxxxxxxxx> wrote:
> > > > >
> > > > >
> > > > > On Thu, Nov 17, 2016 at 03:29:11PM -0500, Olga Kornievskaia
> > > > > wrote:
> > > > > >
> > > > > >
> > > > > > On Thu, Nov 17, 2016 at 3:17 PM, bfields@xxxxxxxxxxxx
> > > > > > <bfields@xxxxxxxxxxxx> wrote:
> > > > > > >
> > > > > > >
> > > > > > > On Thu, Nov 17, 2016 at 02:58:12PM -0500, Olga
> > > > > > > Kornievskaia
> > > > > > > wrote:
> > > > > > > >
> > > > > > > >
> > > > > > > > On Thu, Nov 17, 2016 at 2:32 PM, bfields@xxxxxxxxxxxx
> > > > > > > > <bfields@xxxxxxxxxxxx> wrote:
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > On Thu, Nov 17, 2016 at 05:45:52PM +0000, Trond
> > > > > > > > > Myklebust
> > > > > > > > > wrote:
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > On Thu, 2016-11-17 at 11:31 -0500, J. Bruce Fields
> > > > > > > > > > wrote:
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > > On Wed, Nov 16, 2016 at 02:55:05PM -0600, Jason L
> > > > > > > > > > > Tibbitts III wrote:
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > > I'm replying to a rather old message, but the
> > > > > > > > > > > > issue
> > > > > > > > > > > > has just now
> > > > > > > > > > > > popped
> > > > > > > > > > > > back up again.
> > > > > > > > > > > >
> > > > > > > > > > > > To recap, a client stops being able to access
> > > > > > > > > > > > _any_
> > > > > > > > > > > > mount on a
> > > > > > > > > > > > particular server, and "NFS:
> > > > > > > > > > > > nfs4_reclaim_open_state: Lock reclaim
> > > > > > > > > > > > failed!" appears several hundred times per
> > > > > > > > > > > > second
> > > > > > > > > > > > in the kernel
> > > > > > > > > > > > log.
> > > > > > > > > > > > The load goes up by one for ever process
> > > > > > > > > > > > attempting
> > > > > > > > > > > > to access any
> > > > > > > > > > > > mount
> > > > > > > > > > > > from that particular server. Mounts to other
> > > > > > > > > > > > servers are fine, and
> > > > > > > > > > > > other clients can mount things from that one
> > > > > > > > > > > > server
> > > > > > > > > > > > without
> > > > > > > > > > > > problems.
> > > > > > > > > > > >
> > > > > > > > > > > > When I kill every process keeping that
> > > > > > > > > > > > particular
> > > > > > > > > > > > mount active and
> > > > > > > > > > > > then
> > > > > > > > > > > > umount it, I see:
> > > > > > > > > > > >
> > > > > > > > > > > > NFS: nfs4_reclaim_open_state: unhandled error
> > > > > > > > > > > > -10068
> > > > > > > > > > >
> > > > > > > > > > > NFS4ERR_RETRY_UNCACHED_REP.
> > > > > > > > > > >
> > > > > > > > > > > So, you're using NFSv4.1 or 4.2, and the server
> > > > > > > > > > > thinks that the
> > > > > > > > > > > client
> > > > > > > > > > > has reused a (slot, sequence number) pair, but
> > > > > > > > > > > the
> > > > > > > > > > > server doesn't
> > > > > > > > > > > have a
> > > > > > > > > > > cached response to return.
> > > > > > > > > > >
> > > > > > > > > > > Hard to know how that happened, and it's not
> > > > > > > > > > > shown in
> > > > > > > > > > > the below.
> > > > > > > > > > > Sounds like a bug, though.
> > > > > > > > > >
> > > > > > > > > > ...or a Ctrl-C....
> > > > > > > > >
> > > > > > > > > How does that happen?
> > > > > > > > >
> > > > > > > >
> > > > > > > > If I may chime in...
> > > > > > > >
> > > > > > > > Bruce, when an application sends a Ctrl-C and clients's
> > > > > > > > session slot
> > > > > > > > has sent out an RPC but didn't process the reply, the
> > > > > > > > client doesn't
> > > > > > > > know if the server processed that sequence id or not.
> > > > > > > > In
> > > > > > > > that case,
> > > > > > > > the client doesn't increment the sequence number.
> > > > > > > > Normally
> > > > > > > > the client
> > > > > > > > would handle getting such an error by retrying again
> > > > > > > > (and
> > > > > > > > resetting
> > > > > > > > the slots) but I think during recovery operation the
> > > > > > > > client
> > > > > > > > handles
> > > > > > > > errors differently (by just erroring). I believe the
> > > > > > > > reasoning that we
> > > > > > > > don't want to be stuck trying to recover from the
> > > > > > > > recovery
> > > > > > > > from the
> > > > > > > > recovery etc...
> > > > > > >
> > > > > > > So in that case the client can end up sending a different
> > > > > > > rpc
> > > > > > > reusing
> > > > > > > the old slot and sequence number?
> > > > > >
> > > > > > Correct.
> > > > >
> > > > > So that could get UNCACHED_REP as the response. But if
> > > > > you're
> > > > > very
> > > > > unlucky, couldn't this also happen?:
> > > > >
> > > > > 1) the compound previously sent on that slot was
> > > > > processed by
> > > > > the server and cached
> > > > > 2) the compound you're sending now happens to have
> > > > > the
> > > > > same set
> > > > > of operations
> > > > >
> > > > > with the result that the client doesn't detect that the reply
> > > > > was
> > > > > actually to some other rpc, and instead it returns bad data
> > > > > to
> > > > > the
> > > > > application?
> > > >
> > > > If you are sending exactly the same operations and arguments,
> > > > then
> > > > why
> > > > is a reply from the cache would lead to bad data?
> > >
> > > That would probably be fine, I was wondering what would happen if
> > > you
> > > sent the same operation but different arguments.
> >
> > >
> > > So the original cancelled operation is something like
> > > PUTFH(fh1)+OPEN("foo")+GETFH, and the new one is
> > > PUTFH(fh2)+OPEN("bar")+GETFH. In theory couldn't the second one
> > > succeed
> > > and leave the client thinking it had opened (fh2, bar) when the
> > > filehandle it got back was really for (fh1, foo)?
> > >
> >
> > The client would receive a filehandle for fh1/"foo", so it would
> > apply
> > any state it thought it had received to that file. However,
> > normally,
> > I'd expect to see a NFS4ERR_FALSE_RETRY in this case.
>
> I see Bruce's point that if the server only looks up the cache based
> on the seqid and slot# and doesn't have like a hash of the content
> which I could see is expensive, then the client in this case would
> get
> into trouble of thinking it opened "bar" but really it's "foo". Spec
> says:
>
> Section 18.46.3
> If the client reuses a slot ID and sequence ID for a completely
> different request, the server MAY treat the request as if it is a
> retry of what it has already executed. The server MAY however
> detect
> the client's illegal reuse and return NFS4ERR_SEQ_FALSE_RETRY.
>
> What is "a completely different request". From the client's point of
> view sending different args would constitute a different request. But
> in any case it's a "MAY" so client can't depend on this being
> implemented.
>
What's the alternative? Assume the client pre-emptively bumps the seqid
instead of retrying, then the user presses Ctrl-C again. Repeat a few
more times. How do I now resync the seqids between the client and
server other than by trashing the session?��.n��������+%������w��{.n�����{��w��� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
