[PATCH] f2fs: fix multiple f2fs_add_link() calls having same name

[Jaegeuk Kim]

VFS uses f2fs_lookup() to decide f2fs_add_link() call during file creation.
But, if there is a race condition, f2fs_add_link() can be called multiple
times, resulting in multiple dentries with a same name. This patches fixes
it by adding __f2fs_find_entry() in f2fs_add_link() path.

Cc: <sta...@vger.kernel.org>
Signed-off-by: Jaegeuk Kim <jaeg...@kernel.org>
---
 fs/f2fs/dir.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
index 827c5daef4fc..bc7c48839bec 100644
--- a/fs/f2fs/dir.c
+++ b/fs/f2fs/dir.c
@@ -643,14 +643,24 @@ int __f2fs_add_link(struct inode *dir, const struct qstr 
*name,
                                struct inode *inode, nid_t ino, umode_t mode)
 {
        struct fscrypt_name fname;
+       struct page *page;
+       struct f2fs_dir_entry *de;
        int err;
 
        err = fscrypt_setup_filename(dir, name, 0, &fname);
        if (err)
                return err;
 
-       err = __f2fs_do_add_link(dir, &fname, inode, ino, mode);
-
+       de = __f2fs_find_entry(dir, &fname, &page);
+       if (de) {
+               f2fs_dentry_kunmap(dir, page);
+               f2fs_put_page(page, 0);
+               err = -EEXIST;
+       } else if (!IS_ERR(page)) {
+               err = __f2fs_do_add_link(dir, &fname, inode, ino, mode);
+       } else {
+               err = PTR_ERR(page);
+       }
        fscrypt_free_filename(&fname);
        return err;
 }
-- 
2.11.0