gfs2: clean up iopen glock mess in gfs2_create_inode

Before this patch, gfs2_create_inode had a use-after-free for the
iopen glock in some error paths because it did this:

	gfs2_glock_put(io_gl);
fail_gunlock2:
	if (io_gl)
		clear_bit(GLF_INODE_CREATING, &io_gl->gl_flags);

In some cases, the io_gl was used for create and only had one
reference, so the glock might be freed before the clear_bit().
This patch tries to straighten it out by only jumping to the
error paths where iopen is properly set, and moving the
gfs2_glock_put after the clear_bit.
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/inode.c

@@ -712,7 +712,7 @@ static int gfs2_create_inode(struct inode *dir, struct dentry *dentry,
 
 	error = gfs2_trans_begin(sdp, blocks, 0);
 	if (error)
-		goto fail_gunlock2;
+		goto fail_free_inode;
 
 	if (blocks > 1) {
 		ip->i_eattr = ip->i_no_addr + 1;
@@ -723,7 +723,7 @@ static int gfs2_create_inode(struct inode *dir, struct dentry *dentry,
 
 	error = gfs2_glock_get(sdp, ip->i_no_addr, &gfs2_iopen_glops, CREATE, &io_gl);
 	if (error)
-		goto fail_gunlock2;
+		goto fail_free_inode;
 
 	BUG_ON(test_and_set_bit(GLF_INODE_CREATING, &io_gl->gl_flags));
 
@@ -732,7 +732,6 @@ static int gfs2_create_inode(struct inode *dir, struct dentry *dentry,
 		goto fail_gunlock2;
 
 	glock_set_object(ip->i_iopen_gh.gh_gl, ip);
-	gfs2_glock_put(io_gl);
 	gfs2_set_iop(inode);
 	insert_inode_hash(inode);
 
@@ -765,6 +764,8 @@ static int gfs2_create_inode(struct inode *dir, struct dentry *dentry,
 
 	mark_inode_dirty(inode);
 	d_instantiate(dentry, inode);
+	/* After instantiate, errors should result in evict which will destroy
+	 * both inode and iopen glocks properly. */
 	if (file) {
 		file->f_mode |= FMODE_CREATED;
 		error = finish_open(file, dentry, gfs2_open_common);
@@ -772,15 +773,15 @@ static int gfs2_create_inode(struct inode *dir, struct dentry *dentry,
 	gfs2_glock_dq_uninit(ghs);
 	gfs2_glock_dq_uninit(ghs + 1);
 	clear_bit(GLF_INODE_CREATING, &io_gl->gl_flags);
+	gfs2_glock_put(io_gl);
 	return error;
 
 fail_gunlock3:
 	glock_clear_object(io_gl, ip);
 	gfs2_glock_dq_uninit(&ip->i_iopen_gh);
-	gfs2_glock_put(io_gl);
 fail_gunlock2:
-	if (io_gl)
 	clear_bit(GLF_INODE_CREATING, &io_gl->gl_flags);
+	gfs2_glock_put(io_gl);
 fail_free_inode:
 	if (ip->i_gl) {
 		glock_clear_object(ip->i_gl, ip);