xfs: fix inode lookup race

[firefly-linux-kernel-4.4.55.git] / fs / xfs / xfs_iget.c

diff --git a/fs/xfs/xfs_iget.c b/fs/xfs/xfs_iget.c
index 3631783b2b5385ee939a61e5cafd5b06ef6b0a45..ca752f05c31c498b8ef6b1fc29c6e4ebe2ea6a33 100644 (file)
--- a/fs/xfs/xfs_iget.c
+++ b/fs/xfs/xfs_iget.c
@@ -356,9 +356,20 @@ xfs_iget_cache_miss(
                        BUG();
        }
 
-       spin_lock(&pag->pag_ici_lock);
+       /*
+        * These values must be set before inserting the inode into the radix
+        * tree as the moment it is inserted a concurrent lookup (allowed by the
+        * RCU locking mechanism) can find it and that lookup must see that this
+        * is an inode currently under construction (i.e. that XFS_INEW is set).
+        * The ip->i_flags_lock that protects the XFS_INEW flag forms the
+        * memory barrier that ensures this detection works correctly at lookup
+        * time.
+        */
+       ip->i_udquot = ip->i_gdquot = NULL;
+       xfs_iflags_set(ip, XFS_INEW);
 
        /* insert the new inode */
+       spin_lock(&pag->pag_ici_lock);
        error = radix_tree_insert(&pag->pag_ici_root, agino, ip);
        if (unlikely(error)) {
                WARN_ON(error != -EEXIST);
@@ -366,11 +377,6 @@ xfs_iget_cache_miss(
                error = EAGAIN;
                goto out_preload_end;
        }
-
-       /* These values _must_ be set before releasing the radix tree lock! */
-       ip->i_udquot = ip->i_gdquot = NULL;
-       xfs_iflags_set(ip, XFS_INEW);
-
        spin_unlock(&pag->pag_ici_lock);
        radix_tree_preload_end();