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Diffstat (limited to 'fs/btrfs/tree-log.c')
-rw-r--r--fs/btrfs/tree-log.c36
1 files changed, 27 insertions, 9 deletions
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 29b82a795522..8a6cc600bf18 100644
--- 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;
@@ -3104,18 +3106,26 @@ 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
* new positions. so it's safe to allow log writers to go in.
@@ -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);