lingering caps outstanding after client shutdown?

[Jeff Layton <jlayton@redhat.com>]

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In order to get the correct semantics for a delegation or oplock, we
need to be able to break delegations on open. Cephfs' open routine is
pretty light with the caps though.

One way to fix that is to request a enough caps to cause a delegation
break if any are outstanding. So, I've been playing with the attached
patch. It may be wrong and not what we want, but it seems like it ought
to work.

This patch however causes the LibCephFS.Fchmod test to hang, waiting on
caps, iff the DoubleChmod test is run before it. If you run just Fchmod
test, it works fine. They both use the same filename and hence the same
inode.

The test hangs at the first Fchmod test ceph_open call, waiting for the
caps. At that point though, there should be no other clients accessing
the mount. Is it possible that outstanding caps granted to the client
from the earlier test could be surviving a ceph_shutdown, such that it
blocks the next client from getting them?

To reproduce I've been running this on a build with the attached patch
vs. a vstart cluster:

    $ ./bin/ceph_test_libcephfs --gtest_filter=LibCephFS.DoubleChmod:LibCephFS.Fchmod

I'll continue to dig into this, but I'm starting to wonder if this is
exposing a bug in the mds. Should I open a tracker bug on this?
-- 
Jeff Layton <jlayton@redhat.com>

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From 6f2d562f06529631235bea02b821f83a1a3d0e73 Mon Sep 17 00:00:00 2001
From: Jeffrey Layton <jlayton@ceres.poochiereds.net>
Date: Mon, 25 Sep 2017 15:09:48 -0400
Subject: [PATCH] client: request caps on open

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 src/client/Client.cc | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/src/client/Client.cc b/src/client/Client.cc
index 78517c808a..ffe877fdf8 100644
--- a/src/client/Client.cc
+++ b/src/client/Client.cc
@@ -8425,11 +8425,22 @@ int Client::_open(Inode *in, int flags, mode_t mode, Fh **fhp,
 
   in->get_open_ref(cmode);  // make note of pending open, since it effects _wanted_ caps.
 
-  if ((flags & O_TRUNC) == 0 &&
-      in->caps_issued_mask(want)) {
+  if ((flags & O_TRUNC) == 0 && in->caps_issued_mask(want)) {
     // update wanted?
     check_caps(in, CHECK_CAPS_NODELAY);
   } else {
+    int need = 0, have;
+
+    /* Wait on minimal caps, just to break delegations */
+    if (cmode & CEPH_FILE_MODE_WR)
+      need |= CEPH_CAP_FILE_WR;
+    if (cmode & CEPH_FILE_MODE_RD)
+      need |= CEPH_CAP_FILE_RD;
+
+    result = get_caps(in, need, want, &have, -1);
+    if (result < 0)
+      return result;
+
     MetaRequest *req = new MetaRequest(CEPH_MDS_OP_OPEN);
     filepath path;
     in->make_nosnap_relative_path(path);
@@ -8444,6 +8455,7 @@ int Client::_open(Inode *in, int flags, mode_t mode, Fh **fhp,
     req->head.args.open.old_size = in->size;   // for O_TRUNC
     req->set_inode(in);
     result = make_request(req, perms);
+    put_cap_ref(in, need);
   }
 
   // success?
-- 
2.13.5