f2fs: Create COW inode from parent dentry for atomic write

The i_pino in f2fs_inode_info has the previous parent's i_ino when inode
was renamed, which may cause f2fs_ioc_start_atomic_write to fail.
If file_wrong_pino is true and i_nlink is 1, then to find a valid pino,
we should refer to the dentry from inode.

To resolve this issue, let's get parent inode using parent dentry
directly.

Fixes: 3db1de0e ("f2fs: change the current atomic write way")
Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
Reviewed-by: Sunmin Jeong <s_min.jeong@samsung.com>
Signed-off-by: Yeongjin Gil <youngjin.gil@samsung.com>
Reviewed-by: Daeho Jeong <daehojeong@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -2127,7 +2127,6 @@ static int f2fs_ioc_start_atomic_write(struct file *filp, bool truncate)
 	struct mnt_idmap *idmap = file_mnt_idmap(filp);
 	struct f2fs_inode_info *fi = F2FS_I(inode);
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
-	struct inode *pinode;
 	loff_t isize;
 	int ret;
 
@@ -2180,15 +2179,10 @@ static int f2fs_ioc_start_atomic_write(struct file *filp, bool truncate)
 	/* Check if the inode already has a COW inode */
 	if (fi->cow_inode == NULL) {
 		/* Create a COW inode for atomic write */
-		pinode = f2fs_iget(inode->i_sb, fi->i_pino);
-		if (IS_ERR(pinode)) {
-			f2fs_up_write(&fi->i_gc_rwsem[WRITE]);
-			ret = PTR_ERR(pinode);
-			goto out;
-		}
+		struct dentry *dentry = file_dentry(filp);
+		struct inode *dir = d_inode(dentry->d_parent);
 
-		ret = f2fs_get_tmpfile(idmap, pinode, &fi->cow_inode);
-		iput(pinode);
+		ret = f2fs_get_tmpfile(idmap, dir, &fi->cow_inode);
 		if (ret) {
 			f2fs_up_write(&fi->i_gc_rwsem[WRITE]);
 			goto out;