ceph: improve reference tracking for snaprealm

When snaprealm is created, its initial reference count is zero.
But in some rare cases, the newly created snaprealm is not referenced
by anyone. This causes snaprealm with zero reference count not freed.

The fix is set reference count of newly snaprealm to 1. The reference
is return the function who requests to create the snaprealm. When the
function finishes its job, it releases the reference.

Signed-off-by: Yan, Zheng <zyan@redhat.com>

1 files changed, 16 insertions, 8 deletions

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index d0618e8412fd..8ed1192606d9 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -577,7 +577,6 @@ void ceph_add_cap(struct inode *inode,
                 struct ceph_snap_realm *realm = ceph_lookup_snap_realm(mdsc,
                                                                realmino);
                 if (realm) {
-                        ceph_get_snap_realm(mdsc, realm);
                         spin_lock(&realm->inodes_with_caps_lock);
                         ci->i_snap_realm = realm;
                         list_add(&ci->i_snap_realm_item,
@@ -2447,13 +2446,13 @@ static void invalidate_aliases(struct inode *inode)
  */
 static void handle_cap_grant(struct ceph_mds_client *mdsc,
                              struct inode *inode, struct ceph_mds_caps *grant,
-                             void *snaptrace, int snaptrace_len,
                              u64 inline_version,
                              void *inline_data, int inline_len,
                              struct ceph_buffer *xattr_buf,
                              struct ceph_mds_session *session,
                              struct ceph_cap *cap, int issued)
         __releases(ci->i_ceph_lock)
+        __releases(mdsc->snap_rwsem)
 {
         struct ceph_inode_info *ci = ceph_inode(inode);
         int mds = session->s_mds;
@@ -2654,10 +2653,6 @@ static void handle_cap_grant(struct ceph_mds_client *mdsc,
         spin_unlock(&ci->i_ceph_lock);
 
         if (le32_to_cpu(grant->op) == CEPH_CAP_OP_IMPORT) {
-                down_write(&mdsc->snap_rwsem);
-                ceph_update_snap_trace(mdsc, snaptrace,
-                                       snaptrace + snaptrace_len, false);
-                downgrade_write(&mdsc->snap_rwsem);
                 kick_flushing_inode_caps(mdsc, session, inode);
                 up_read(&mdsc->snap_rwsem);
                 if (newcaps & ~issued)
@@ -3067,6 +3062,7 @@ void ceph_handle_caps(struct ceph_mds_session *session,
         struct ceph_cap *cap;
         struct ceph_mds_caps *h;
         struct ceph_mds_cap_peer *peer = NULL;
+        struct ceph_snap_realm *realm;
         int mds = session->s_mds;
         int op, issued;
         u32 seq, mseq;
@@ -3168,11 +3164,23 @@ void ceph_handle_caps(struct ceph_mds_session *session,
                 goto done_unlocked;
 
         case CEPH_CAP_OP_IMPORT:
+                realm = NULL;
+                if (snaptrace_len) {
+                        down_write(&mdsc->snap_rwsem);
+                        ceph_update_snap_trace(mdsc, snaptrace,
+                                               snaptrace + snaptrace_len,
+                                               false, &realm);
+                        downgrade_write(&mdsc->snap_rwsem);
+                } else {
+                        down_read(&mdsc->snap_rwsem);
+                }
                 handle_cap_import(mdsc, inode, h, peer, session,
                                   &cap, &issued);
-                handle_cap_grant(mdsc, inode, h,  snaptrace, snaptrace_len,
+                handle_cap_grant(mdsc, inode, h,
                                  inline_version, inline_data, inline_len,
                                  msg->middle, session, cap, issued);
+                if (realm)
+                        ceph_put_snap_realm(mdsc, realm);
                 goto done_unlocked;
         }
 
@@ -3192,7 +3200,7 @@ void ceph_handle_caps(struct ceph_mds_session *session,
         case CEPH_CAP_OP_GRANT:
                 __ceph_caps_issued(ci, &issued);
                 issued |= __ceph_caps_dirty(ci);
-                handle_cap_grant(mdsc, inode, h, NULL, 0,
+                handle_cap_grant(mdsc, inode, h,
                                  inline_version, inline_data, inline_len,
                                  msg->middle, session, cap, issued);
                 goto done_unlocked;