mds: drop locks and retry when lock set changes

An optimization was added to avoid an unnecessary gather on the inode
filelock when the client can safely get the file size without also
getting issued the requested caps. However, if a retry of getattr
is necessary, this conditional inclusion of the inode filelock
can cause lock-order violations resulting in deadlock.

So, if we've already acquired some of the inode's locks then we must
drop locks and retry.

Fixes: https://tracker.ceph.com/issues/62052
Fixes: c822b3e2573578c288d170d1031672b74e02dced
Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>
(cherry picked from commit b5719ac32fe6431131842d62ffaf7101c03e9bac)

diff --git a/src/mds/Server.cc b/src/mds/Server.cc
index 82f2a2e5e6587d2a79085a53586d1e1a3bf8d93b..188c7728416d25d3262415f7237fb3c0be09e7d8 100644 (file)
--- a/src/mds/Server.cc
+++ b/src/mds/Server.cc
@@ -4071,6 +4071,24 @@ void Server::handle_client_getattr(MDRequestRef& mdr, bool is_lookup)
     } else if (ref->filelock.is_stable() ||
               ref->filelock.get_num_wrlocks() > 0 ||
               !ref->filelock.can_read(mdr->get_client())) {
+      /* Since we're taking advantage of an optimization here:
+       *
+       * We cannot suddenly, due to a changing condition, add this filelock as
+       * it can cause lock-order deadlocks. In this case, that condition is the
+       * lock state changes between request retries. If that happens, we need
+       * to check if we've acquired the other locks in this vector. If we have,
+       * then we need to drop those locks and retry.
+       */
+      if (mdr->is_rdlocked(&ref->linklock) ||
+          mdr->is_rdlocked(&ref->authlock) ||
+          mdr->is_rdlocked(&ref->xattrlock)) {
+        /* start over */
+        dout(20) << " dropping locks and restarting request because filelock state change" << dendl;
+       mds->locker->drop_locks(mdr.get());
+       mdr->drop_local_auth_pins();
+       mds->queue_waiter(new C_MDS_RetryRequest(mdcache, mdr));
+        return;
+      }
       lov.add_rdlock(&ref->filelock);
       mdr->locking_state &= ~MutationImpl::ALL_LOCKED;
     }