3 files changed, 23 insertions, 11 deletions

diff --git a/fs/xfs/linux-2.6/xfs_sync.c b/fs/xfs/linux-2.6/xfs_sync.c
index 81976ffed7d6..3a1d229b4784 100644
--- a/fs/xfs/linux-2.6/xfs_sync.c
+++ b/fs/xfs/linux-2.6/xfs_sync.c
@@ -150,17 +150,17 @@ xfs_inode_ag_iter_next_pag(
                 int found;
                 int ref;
 
-                spin_lock(&mp->m_perag_lock);
+                rcu_read_lock();
                 found = radix_tree_gang_lookup_tag(&mp->m_perag_tree,
                                 (void **)&pag, *first, 1, tag);
                 if (found <= 0) {
-                        spin_unlock(&mp->m_perag_lock);
+                        rcu_read_unlock();
                         return NULL;
                 }
                 *first = pag->pag_agno + 1;
                 /* open coded pag reference increment */
                 ref = atomic_inc_return(&pag->pag_ref);
-                spin_unlock(&mp->m_perag_lock);
+                rcu_read_unlock();
                 trace_xfs_perag_get_reclaim(mp, pag->pag_agno, ref, _RET_IP_);
         } else {
                 pag = xfs_perag_get(mp, *first);
diff --git a/fs/xfs/xfs_ag.h b/fs/xfs/xfs_ag.h
index 4917d4eed4ed..51c42c202bf1 100644
--- a/fs/xfs/xfs_ag.h
+++ b/fs/xfs/xfs_ag.h
@@ -230,6 +230,9 @@ typedef struct xfs_perag {
         rwlock_t        pag_ici_lock;   /* incore inode lock */
         struct radix_tree_root pag_ici_root;    /* incore inode cache root */
         int             pag_ici_reclaimable;    /* reclaimable inodes */
+
+        /* for rcu-safe freeing */
+        struct rcu_head rcu_head;
 #endif
         int             pagb_count;     /* pagb slots in use */
 } xfs_perag_t;
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index 00c7a876807d..14fc6e9e1816 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -199,6 +199,8 @@ xfs_uuid_unmount(
 
 /*
  * Reference counting access wrappers to the perag structures.
+ * Because we never free per-ag structures, the only thing we
+ * have to protect against changes is the tree structure itself.
  */
 struct xfs_perag *
 xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t agno)
@@ -206,13 +208,13 @@ xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t agno)
         struct xfs_perag        *pag;
         int                     ref = 0;
 
-        spin_lock(&mp->m_perag_lock);
+        rcu_read_lock();
         pag = radix_tree_lookup(&mp->m_perag_tree, agno);
         if (pag) {
                 ASSERT(atomic_read(&pag->pag_ref) >= 0);
                 ref = atomic_inc_return(&pag->pag_ref);
         }
-        spin_unlock(&mp->m_perag_lock);
+        rcu_read_unlock();
         trace_xfs_perag_get(mp, agno, ref, _RET_IP_);
         return pag;
 }
@@ -227,10 +229,18 @@ xfs_perag_put(struct xfs_perag *pag)
         trace_xfs_perag_put(pag->pag_mount, pag->pag_agno, ref, _RET_IP_);
 }
 
+STATIC void
+__xfs_free_perag(
+        struct rcu_head *head)
+{
+        struct xfs_perag *pag = container_of(head, struct xfs_perag, rcu_head);
+
+        ASSERT(atomic_read(&pag->pag_ref) == 0);
+        kmem_free(pag);
+}
+
 /*
- * Free up the resources associated with a mount structure.  Assume that
- * the structure was initially zeroed, so we can tell which fields got
- * initialized.
+ * Free up the per-ag resources associated with the mount structure.
  */
 STATIC void
 xfs_free_perag(
@@ -242,10 +252,9 @@ xfs_free_perag(
         for (agno = 0; agno < mp->m_sb.sb_agcount; agno++) {
                 spin_lock(&mp->m_perag_lock);
                 pag = radix_tree_delete(&mp->m_perag_tree, agno);
-                ASSERT(pag);
-                ASSERT(atomic_read(&pag->pag_ref) == 0);
                 spin_unlock(&mp->m_perag_lock);
-                kmem_free(pag);
+                ASSERT(pag);
+                call_rcu(&pag->rcu_head, __xfs_free_perag);
         }
 }