Merge tag 'for-5.4-rc2-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave...

[linux-2.6-microblaze.git] / fs / btrfs / tree-log.c

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 29b82a7..8a6cc60 100644 (file)
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -2932,7 +2932,8 @@ out:
  * in the tree of log roots
  */
 static int update_log_root(struct btrfs_trans_handle *trans,
-                          struct btrfs_root *log)
+                          struct btrfs_root *log,
+                          struct btrfs_root_item *root_item)
 {
        struct btrfs_fs_info *fs_info = log->fs_info;
        int ret;
@@ -2940,10 +2941,10 @@ static int update_log_root(struct btrfs_trans_handle *trans,
        if (log->log_transid == 1) {
                /* insert root item on the first sync */
                ret = btrfs_insert_root(trans, fs_info->log_root_tree,
-                               &log->root_key, &log->root_item);
+                               &log->root_key, root_item);
        } else {
                ret = btrfs_update_root(trans, fs_info->log_root_tree,
-                               &log->root_key, &log->root_item);
+                               &log->root_key, root_item);
        }
        return ret;
 }
@@ -3041,6 +3042,7 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_root *log = root->log_root;
        struct btrfs_root *log_root_tree = fs_info->log_root_tree;
+       struct btrfs_root_item new_root_item;
        int log_transid = 0;
        struct btrfs_log_ctx root_log_ctx;
        struct blk_plug plug;
@@ -3104,17 +3106,25 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
                goto out;
        }
 
+       /*
+        * We _must_ update under the root->log_mutex in order to make sure we
+        * have a consistent view of the log root we are trying to commit at
+        * this moment.
+        *
+        * We _must_ copy this into a local copy, because we are not holding the
+        * log_root_tree->log_mutex yet.  This is important because when we
+        * commit the log_root_tree we must have a consistent view of the
+        * log_root_tree when we update the super block to point at the
+        * log_root_tree bytenr.  If we update the log_root_tree here we'll race
+        * with the commit and possibly point at the new block which we may not
+        * have written out.
+        */
        btrfs_set_root_node(&log->root_item, log->node);
+       memcpy(&new_root_item, &log->root_item, sizeof(new_root_item));
 
        root->log_transid++;
        log->log_transid = root->log_transid;
        root->log_start_pid = 0;
-       /*
-        * Update or create log root item under the root's log_mutex to prevent
-        * races with concurrent log syncs that can lead to failure to update
-        * log root item because it was not created yet.
-        */
-       ret = update_log_root(trans, log);
        /*
         * IO has been started, blocks of the log tree have WRITTEN flag set
         * in their headers. new modifications of the log will be written to
@@ -3135,6 +3145,14 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
        mutex_unlock(&log_root_tree->log_mutex);
 
        mutex_lock(&log_root_tree->log_mutex);
+
+       /*
+        * Now we are safe to update the log_root_tree because we're under the
+        * log_mutex, and we're a current writer so we're holding the commit
+        * open until we drop the log_mutex.
+        */
+       ret = update_log_root(trans, log, &new_root_item);
+
        if (atomic_dec_and_test(&log_root_tree->log_writers)) {
                /* atomic_dec_and_test implies a barrier */
                cond_wake_up_nomb(&log_root_tree->log_writer_wait);