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/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 "