Unionfs: mmap fixes

Ensure we have lower inodes in prepare/commit_write.

Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>

diff --git a/fs/unionfs/mmap.c b/fs/unionfs/mmap.c
index a0e654bef667eefa167bc1c1300fe43fa0bba196..ad770acfbc42cb45296dc9b1a629a4f0e972be67 100644 (file)
--- a/fs/unionfs/mmap.c
+++ b/fs/unionfs/mmap.c
@@ -224,13 +224,26 @@ out:
 static int unionfs_prepare_write(struct file *file, struct page *page,
                                 unsigned from, unsigned to)
 {
+       int err;
+
+       unionfs_read_lock(file->f_path.dentry->d_sb, UNIONFS_SMUTEX_PARENT);
        /*
-        * Just copy lower inode attributes and return success.  Not much
-        * else to do here.  No need to lock either (lockdep won't like it).
-        * Let commit_write do all the hard work instead.
+        * This is the only place where we unconditionally copy the lower
+        * attribute times before calling unionfs_file_revalidate.  The
+        * reason is that our ->write calls do_sync_write which in turn will
+        * call our ->prepare_write and then ->commit_write.  Before our
+        * ->write is called, the lower mtimes are in sync, but by the time
+        * the VFS calls our ->commit_write, the lower mtimes have changed.
+        * Therefore, the only reasonable time for us to sync up from the
+        * changed lower mtimes, and avoid an invariant violation warning,
+        * is here, in ->prepare_write.
         */
        unionfs_copy_attr_times(file->f_path.dentry->d_inode);
-       return 0;
+       err = unionfs_file_revalidate(file, true);
+       unionfs_check_file(file);
+       unionfs_read_unlock(file->f_path.dentry->d_sb);
+
+       return err;
 }
 
 static int unionfs_commit_write(struct file *file, struct page *page,
@@ -252,7 +265,6 @@ static int unionfs_commit_write(struct file *file, struct page *page,
        unionfs_check_file(file);
 
        inode = page->mapping->host;
-       lower_inode = unionfs_lower_inode(inode);
 
        if (UNIONFS_F(file) != NULL)
                lower_file = unionfs_lower_file(file);
@@ -282,6 +294,10 @@ static int unionfs_commit_write(struct file *file, struct page *page,
                goto out;
 
        /* if vfs_write succeeded above, sync up our times/sizes */
+       lower_inode = lower_file->f_path.dentry->d_inode;
+       if (!lower_inode)
+               lower_inode = unionfs_lower_inode(inode);
+       BUG_ON(!lower_inode);
        fsstack_copy_inode_size(inode, lower_inode);
        unionfs_copy_attr_times(inode);
        mark_inode_dirty_sync(inode);