[DLM] Don't delete misc device if lockspace removal fails

Currently if the lockspace removal fails the misc device associated with a
lockspace is left deleted. After that there is no way to access the orphaned
lockspace from userland.

This patch recreates the misc device if th dlm_release_lockspace fails. I
believe this is better than attempting to remove the lockspace first because
that leaves an unattached device lying around. The potential gap in which there
is no access to the lockspace between removing the misc device and recreating it
is acceptable ... after all the application is trying to remove it, and only new
users of the lockspace will be affected.
Signed-Off-By: Patrick Caulfield <pcaulfie@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/dlm/user.c

@@ -286,47 +286,55 @@ static int device_user_unlock(struct dlm_user_proc *proc,
 	return error;
 }
 
-static int device_create_lockspace(struct dlm_lspace_params *params)
+static int create_misc_device(struct dlm_ls *ls, char *name)
 {
-	dlm_lockspace_t *lockspace;
-	struct dlm_ls *ls;
 	int error, len;
 
-	if (!capable(CAP_SYS_ADMIN))
-		return -EPERM;
-
-	error = dlm_new_lockspace(params->name, strlen(params->name),
-				  &lockspace, 0, DLM_USER_LVB_LEN);
-	if (error)
-		return error;
-
-	ls = dlm_find_lockspace_local(lockspace);
-	if (!ls)
-		return -ENOENT;
-
 	error = -ENOMEM;
-	len = strlen(params->name) + strlen(name_prefix) + 2;
+	len = strlen(name) + strlen(name_prefix) + 2;
 	ls->ls_device.name = kzalloc(len, GFP_KERNEL);
 	if (!ls->ls_device.name)
 		goto fail;
+
 	snprintf((char *)ls->ls_device.name, len, "%s_%s", name_prefix,
-		 params->name);
+		 name);
 	ls->ls_device.fops = &device_fops;
 	ls->ls_device.minor = MISC_DYNAMIC_MINOR;
 
 	error = misc_register(&ls->ls_device);
 	if (error) {
 		kfree(ls->ls_device.name);
-		goto fail;
 	}
+fail:
+	return error;
+}
 
-	error = ls->ls_device.minor;
-	dlm_put_lockspace(ls);
+static int device_create_lockspace(struct dlm_lspace_params *params)
+{
+	dlm_lockspace_t *lockspace;
+	struct dlm_ls *ls;
+	int error;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	error = dlm_new_lockspace(params->name, strlen(params->name),
+				  &lockspace, 0, DLM_USER_LVB_LEN);
+	if (error)
 		return error;
 
- fail:
+	ls = dlm_find_lockspace_local(lockspace);
+	if (!ls)
+		return -ENOENT;
+
+	error = create_misc_device(ls, params->name);
 	dlm_put_lockspace(ls);
+
+	if (error)
 		dlm_release_lockspace(lockspace, 0);
+	else
+		error = ls->ls_device.minor;
+
 	return error;
 }
 
@@ -343,6 +351,10 @@ static int device_remove_lockspace(struct dlm_lspace_params *params)
 	if (!ls)
 		return -ENOENT;
 
+	/* Deregister the misc device first, so we don't have
+	 * a device that's not attached to a lockspace. If
+	 * dlm_release_lockspace fails then we can recreate it
+	 */
 	error = misc_deregister(&ls->ls_device);
 	if (error) {
 		dlm_put_lockspace(ls);
@@ -361,6 +373,8 @@ static int device_remove_lockspace(struct dlm_lspace_params *params)
 
 	dlm_put_lockspace(ls);
 	error = dlm_release_lockspace(lockspace, force);
+	if (error)
+		create_misc_device(ls, ls->ls_name);
  out:
 	return error;
 }