overlayfs: don't hold ->i_mutex over opening the real directory

just use it to serialize the assignment

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 13 insertions, 6 deletions

diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index c6787f84ece9..b7d9fb098840 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -458,20 +458,27 @@ static int ovl_dir_fsync(struct file *file, loff_t start, loff_t end,
         if (!od->is_upper && ovl_path_type(dentry) == OVL_PATH_MERGE) {
                 struct inode *inode = file_inode(file);
 
-                mutex_lock(&inode->i_mutex);
                 realfile = od->upperfile;
                 if (!realfile) {
                         struct path upperpath;
 
                         ovl_path_upper(dentry, &upperpath);
                         realfile = ovl_path_open(&upperpath, O_RDONLY);
-                        if (IS_ERR(realfile)) {
-                                mutex_unlock(&inode->i_mutex);
-                                return PTR_ERR(realfile);
+                        mutex_lock(&inode->i_mutex);
+                        if (!od->upperfile) {
+                                if (IS_ERR(realfile)) {
+                                        mutex_unlock(&inode->i_mutex);
+                                        return PTR_ERR(realfile);
+                                }
+                                od->upperfile = realfile;
+                        } else {
+                                /* somebody has beaten us to it */
+                                if (!IS_ERR(realfile))
+                                        fput(realfile);
+                                realfile = od->upperfile;
                         }
-                        od->upperfile = realfile;
+                        mutex_unlock(&inode->i_mutex);
                 }
-                mutex_unlock(&inode->i_mutex);
         }
 
         return vfs_fsync_range(realfile, start, end, datasync);