ext4: Make fsync sync new parent directories in no-journal mode

Add a new ext4 state to tell us when a file has been newly created; use
that state in ext4_sync_file in no-journal mode to tell us when we need
to sync the parent directory as well as the inode and data itself.  This
fixes a problem in which a panic or power failure may lose the entire
file even when using fsync, since the parent directory entry is lost.

Addresses-Google-Bug: #2480057

Signed-off-by: Frank Mayhar <fmayhar@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 29 insertions, 2 deletions

diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
index 6ca7b6e59d83..e187f87acec0 100644
--- a/fs/ext4/fsync.c
+++ b/fs/ext4/fsync.c
@@ -35,6 +35,29 @@
 #include <trace/events/ext4.h>
 
 /*
+ * If we're not journaling and this is a just-created file, we have to
+ * sync our parent directory (if it was freshly created) since
+ * otherwise it will only be written by writeback, leaving a huge
+ * window during which a crash may lose the file.  This may apply for
+ * the parent directory's parent as well, and so on recursively, if
+ * they are also freshly created.
+ */
+static void ext4_sync_parent(struct inode *inode)
+{
+        struct dentry *dentry = NULL;
+
+        while (inode && ext4_test_inode_state(inode, EXT4_STATE_NEWENTRY)) {
+                ext4_clear_inode_state(inode, EXT4_STATE_NEWENTRY);
+                dentry = list_entry(inode->i_dentry.next,
+                                    struct dentry, d_alias);
+                if (!dentry || !dentry->d_parent || !dentry->d_parent->d_inode)
+                        break;
+                inode = dentry->d_parent->d_inode;
+                sync_mapping_buffers(inode->i_mapping);
+        }
+}
+
+/*
  * akpm: A new design for ext4_sync_file().
  *
  * This is only called from sys_fsync(), sys_fdatasync() and sys_msync().
@@ -67,8 +90,12 @@ int ext4_sync_file(struct file *file, struct dentry *dentry, int datasync)
         if (ret < 0)
                 return ret;
 
-        if (!journal)
-                return simple_fsync(file, dentry, datasync);
+        if (!journal) {
+                ret = simple_fsync(file, dentry, datasync);
+                if (!ret && !list_empty(&inode->i_dentry))
+                        ext4_sync_parent(inode);
+                return ret;
+        }
 
         /*
          * data=writeback,ordered: