Btrfs: use a lock to protect incompat/compat flag of the super block

[linux-2.6-block.git] / fs / btrfs / ctree.h

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 1a850402937d0fd3263ab77b78e397717ca53867..c3b15f8dca009f4956a965ee00a88d3ec95c9165 100644 (file)
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1362,6 +1362,17 @@ struct btrfs_fs_info {
        wait_queue_head_t transaction_blocked_wait;
        wait_queue_head_t async_submit_wait;
 
+       /*
+        * Used to protect the incompat_flags, compat_flags, compat_ro_flags
+        * when they are updated.
+        *
+        * Because we do not clear the flags for ever, so we needn't use
+        * the lock on the read side.
+        *
+        * We also needn't use the lock when we mount the fs, because
+        * there is no other task which will update the flag.
+        */
+       spinlock_t super_lock;
        struct btrfs_super_block *super_copy;
        struct btrfs_super_block *super_for_commit;
        struct block_device *__bdev;
@@ -3688,8 +3699,15 @@ static inline void __btrfs_set_fs_incompat(struct btrfs_fs_info *fs_info,
        disk_super = fs_info->super_copy;
        features = btrfs_super_incompat_flags(disk_super);
        if (!(features & flag)) {
-               features |= flag;
-               btrfs_set_super_incompat_flags(disk_super, features);
+               spin_lock(&fs_info->super_lock);
+               features = btrfs_super_incompat_flags(disk_super);
+               if (!(features & flag)) {
+                       features |= flag;
+                       btrfs_set_super_incompat_flags(disk_super, features);
+                       printk(KERN_INFO "btrfs: setting %llu feature flag\n",
+                                        flag);
+               }
+               spin_unlock(&fs_info->super_lock);
        }
 }