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>

4 files changed, 14 insertions, 9 deletions

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 8b53193e4f7c..90d789df9ce0 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -641,10 +641,10 @@ static int __cap_is_valid(struct ceph_cap *cap)
         unsigned long ttl;
         u32 gen;
 
-        spin_lock(&cap->session->s_cap_lock);
+        spin_lock(&cap->session->s_gen_ttl_lock);
         gen = cap->session->s_cap_gen;
         ttl = cap->session->s_cap_ttl;
-        spin_unlock(&cap->session->s_cap_lock);
+        spin_unlock(&cap->session->s_gen_ttl_lock);
 
         if (cap->cap_gen < gen || time_after_eq(jiffies, ttl)) {
                 dout("__cap_is_valid %p cap %p issued %s "
diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
index 98954003a8d3..63c52f33361b 100644
--- a/fs/ceph/dir.c
+++ b/fs/ceph/dir.c
@@ -975,10 +975,10 @@ static int dentry_lease_is_valid(struct dentry *dentry)
         di = ceph_dentry(dentry);
         if (di && di->lease_session) {
                 s = di->lease_session;
-                spin_lock(&s->s_cap_lock);
+                spin_lock(&s->s_gen_ttl_lock);
                 gen = s->s_cap_gen;
                 ttl = s->s_cap_ttl;
-                spin_unlock(&s->s_cap_lock);
+                spin_unlock(&s->s_gen_ttl_lock);
 
                 if (di->lease_gen == gen &&
                     time_before(jiffies, dentry->d_time) &&
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;
 
diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index a50ca0e39475..8c7c04ebb595 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -117,10 +117,13 @@ struct ceph_mds_session {
         void             *s_authorizer_buf, *s_authorizer_reply_buf;
         size_t            s_authorizer_buf_len, s_authorizer_reply_buf_len;
 
-        /* protected by s_cap_lock */
-        spinlock_t        s_cap_lock;
+        /* protected by s_gen_ttl_lock */
+        spinlock_t        s_gen_ttl_lock;
         u32               s_cap_gen;  /* inc each time we get mds stale msg */
         unsigned long     s_cap_ttl;  /* when session caps expire */
+
+        /* protected by s_cap_lock */
+        spinlock_t        s_cap_lock;
         struct list_head  s_caps;     /* all caps issued by this session */
         int               s_nr_caps, s_trim_caps;
         int               s_num_cap_releases;