mds: properly setup client_need_snapflush for snap inode

MDCache::cow_inode() checks "cap->issued() & CEPH_CAP_ANY_WR" to decide
if it needs to setup client_need_snapflush for the new snap inode. If
cap message flushes dirty caps and releases the same caps, cap->issued()
may have no WR caps when MDCache::cow_inode() gets called. The solution
is temporarily setting NEEDSNAPFLUSH on Capability::state.

Signed-off-by: "Yan, Zheng" <zyan@redhat.com>

src/mds/Locker.cc

@@ -2892,16 +2892,20 @@ void Locker::handle_client_caps(MClientCaps *m)
 	dout(10) << " revocation in progress, not making any conclusions about null snapflushes" << dendl;
       }
     }
-    if (cap->need_snapflush() && !(m->flags & MClientCaps::FLAG_PENDING_CAPSNAP))
-      cap->clear_needsnapflush();
 
+    bool need_snapflush = cap->need_snapflush();
     if (m->get_dirty() && in->is_auth()) {
       dout(7) << " flush client." << client << " dirty " << ccap_string(m->get_dirty())
 	      << " seq " << m->get_seq() << " on " << *in << dendl;
       ack = new MClientCaps(CEPH_CAP_OP_FLUSH_ACK, in->ino(), 0, cap->get_cap_id(), m->get_seq(),
 			    m->get_caps(), 0, m->get_dirty(), 0, mds->get_osd_epoch_barrier());
       ack->set_client_tid(m->get_client_tid());
       ack->set_oldest_flush_tid(m->get_oldest_flush_tid());
+
+      // client flushes and releases caps at the same time. make sure MDCache::cow_inode()
+      // properly setup CInode::client_need_snapflush
+      if ((m->get_dirty() & ~cap->issued()) && !need_snapflush)
+	cap->mark_needsnapflush();
     }
 
     // filter wanted based on what we could ever give out (given auth/replica status)
@@ -2915,10 +2919,15 @@ void Locker::handle_client_caps(MClientCaps *m)
 
       adjust_cap_wanted(cap, new_wanted, m->get_issue_seq());
     }
-
-    if (in->is_auth() &&
-	_do_cap_update(in, cap, m->get_dirty(), follows, m, ack, &need_flush)) {
-      // updated
+
+    bool updated = in->is_auth() &&
+		   _do_cap_update(in, cap, m->get_dirty(), follows, m, ack, &need_flush);
+
+    if (cap->need_snapflush() &&
+	(!need_snapflush || !(m->flags & MClientCaps::FLAG_PENDING_CAPSNAP)))
+      cap->clear_needsnapflush();
+
+    if (updated) {
       eval(in, CEPH_CAP_LOCKS);
 
       if (!need_flush && (cap->wanted() & ~cap->pending()))