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, 2 insertions, 2 deletions

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) &&