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>
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index be1415fc..a4fdf93 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -400,9 +400,11 @@
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 @@
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;
