ceph: create a new session lock to avoid lock inversion

Lockdep was reporting a possible circular lock dependency in
dentry_lease_is_valid().  That function needs to sample the
session's s_cap_gen and and s_cap_ttl fields coherently, but needs
to do so while holding a dentry lock.  The s_cap_lock field was
being used to protect the two fields, but that can't be taken while
holding a lock on a dentry within the session.

In most cases, the s_cap_gen and s_cap_ttl fields only get operated
on separately.  But in three cases they need to be updated together.
Implement a new lock to protect the spots updating both fields
atomically is required.

Signed-off-by: Alex Elder <elder@dreamhost.com>
Reviewed-by: Sage Weil <sage@newdream.net>

1 files changed, 5 insertions, 3 deletions

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index be1415fcaac8..a4fdf9397a90 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -400,9 +400,11 @@ static struct ceph_mds_session *register_session(struct ceph_mds_client *mdsc,
         s->s_con.peer_name.type = CEPH_ENTITY_TYPE_MDS;
         s->s_con.peer_name.num = cpu_to_le64(mds);
 
-        spin_lock_init(&s->s_cap_lock);
+        spin_lock_init(&s->s_gen_ttl_lock);
         s->s_cap_gen = 0;
         s->s_cap_ttl = 0;
+
+        spin_lock_init(&s->s_cap_lock);
         s->s_renew_requested = 0;
         s->s_renew_seq = 0;
         INIT_LIST_HEAD(&s->s_caps);
@@ -2328,10 +2330,10 @@ static void handle_session(struct ceph_mds_session *session,
         case CEPH_SESSION_STALE:
                 pr_info("mds%d caps went stale, renewing\n",
                         session->s_mds);
-                spin_lock(&session->s_cap_lock);
+                spin_lock(&session->s_gen_ttl_lock);
                 session->s_cap_gen++;
                 session->s_cap_ttl = 0;
-                spin_unlock(&session->s_cap_lock);
+                spin_unlock(&session->s_gen_ttl_lock);
                 send_renew_caps(mdsc, session);
                 break;