cgroup: make cgroup_addrm_files() clean up after itself on failures

After a file creation failure, cgroup_addrm_files() it didn't remove
the files which had already been created.  When cgroup_populate_dir()
is the caller, this is fine as the caller performs cleanup; however,
for other callers, this may leave unactivated dangling files behind.
As kernfs directory removals are recursive, this doesn't lead to
permanent memory leak but it can, for example, fail future attempts to
create those files again.

There's no point in keeping around this sort of subtlety and it gets
in the way of planned updates to file handling.  This patch makes
cgroup_addrm_files() clean up after itself on failures.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>

kernel/cgroup.c

@@ -3255,19 +3255,18 @@ static int cgroup_add_file(struct cgroup *cgrp, struct cftype *cft)
  * @is_add: whether to add or remove
  *
  * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
- * For removals, this function never fails.  If addition fails, this
+ * For removals, this function never fails.
- * function doesn't remove files already added.  The caller is responsible
- * for cleaning up.
  */
 static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
 			      bool is_add)
 {
-	struct cftype *cft;
+	struct cftype *cft, *cft_end = NULL;
 	int ret;
 
 	lockdep_assert_held(&cgroup_mutex);
 
-	for (cft = cfts; cft->name[0] != '\0'; cft++) {
+restart:
+	for (cft = cfts; cft != cft_end && cft->name[0] != '\0'; cft++) {
 		/* does cft->flags tell us to skip this file on @cgrp? */
 		if ((cft->flags & __CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
 			continue;
@@ -3283,7 +3282,9 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
 			if (ret) {
 				pr_warn("%s: failed to add %s, err=%d\n",
 					__func__, cft->name, ret);
-				return ret;
+				cft_end = cft;
+				is_add = false;
+				goto restart;
 			}
 		} else {
 			cgroup_rm_file(cgrp, cft);