ceph: queue cap snap writeback for realm children on snap update

When a realm is updated, we need to queue writeback on inodes in that
realm _and_ its children.  Otherwise, if the inode gets cowed on the
server, we can get a hang later due to out-of-sync cap/snap state.

Signed-off-by: Sage Weil <sage@newdream.net>

1 files changed, 37 insertions, 23 deletions

diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index 2cb190c2bd99..6bdbf3ae7082 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -548,6 +548,41 @@ int __ceph_finish_cap_snap(struct ceph_inode_info *ci,
         return 1;  /* caller may want to ceph_flush_snaps */
 }
 
+/*
+ * Queue cap_snaps for snap writeback for this realm and its children.
+ * Called under snap_rwsem, so realm topology won't change.
+ */
+static void queue_realm_cap_snaps(struct ceph_snap_realm *realm)
+{
+        struct ceph_inode_info *ci;
+        struct inode *lastinode = NULL;
+        struct ceph_snap_realm *child;
+
+        dout("queue_realm_cap_snaps %p %llx inodes\n", realm, realm->ino);
+
+        spin_lock(&realm->inodes_with_caps_lock);
+        list_for_each_entry(ci, &realm->inodes_with_caps,
+                            i_snap_realm_item) {
+                struct inode *inode = igrab(&ci->vfs_inode);
+                if (!inode)
+                        continue;
+                spin_unlock(&realm->inodes_with_caps_lock);
+                if (lastinode)
+                        iput(lastinode);
+                lastinode = inode;
+                ceph_queue_cap_snap(ci);
+                spin_lock(&realm->inodes_with_caps_lock);
+        }
+        spin_unlock(&realm->inodes_with_caps_lock);
+        if (lastinode)
+                iput(lastinode);
+
+        dout("queue_realm_cap_snaps %p %llx children\n", realm, realm->ino);
+        list_for_each_entry(child, &realm->children, child_item)
+                queue_realm_cap_snaps(child);
+
+        dout("queue_realm_cap_snaps %p %llx done\n", realm, realm->ino);
+}
 
 /*
  * Parse and apply a snapblob "snap trace" from the MDS.  This specifies
@@ -598,29 +633,8 @@ more:
                  *
                  * ...unless it's a snap deletion!
                  */
-                if (!deletion) {
-                        struct ceph_inode_info *ci;
-                        struct inode *lastinode = NULL;
-
-                        spin_lock(&realm->inodes_with_caps_lock);
-                        list_for_each_entry(ci, &realm->inodes_with_caps,
-                                            i_snap_realm_item) {
-                                struct inode *inode = igrab(&ci->vfs_inode);
-                                if (!inode)
-                                        continue;
-                                spin_unlock(&realm->inodes_with_caps_lock);
-                                if (lastinode)
-                                        iput(lastinode);
-                                lastinode = inode;
-                                ceph_queue_cap_snap(ci);
-                                spin_lock(&realm->inodes_with_caps_lock);
-                        }
-                        spin_unlock(&realm->inodes_with_caps_lock);
-                        if (lastinode)
-                                iput(lastinode);
-                        dout("update_snap_trace cap_snaps queued\n");
-                }
-
+                if (!deletion)
+                        queue_realm_cap_snaps(realm);
         } else {
                 dout("update_snap_trace %llx %p seq %lld unchanged\n",
                      realm->ino, realm, realm->seq);