cgroup: fix error path of cgroup_addrm_files()

cgroup_addrm_files() mishandled error return value from
cgroup_add_file() and returns error iff the last file fails to create.
As we're in the process of cleaning up file add/rm error handling and
will reliably propagate file creation failures, there's no point in
keeping adding files after a failure.

Replace the broken error collection logic with immediate error return.
While at it, add lockdep assertions and function comment.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 09bfa87..9b16d75 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2780,11 +2780,26 @@ out:
        return error;
 }
 
+/**
+ * cgroup_addrm_files - add or remove files to a cgroup directory
+ * @cgrp: the target cgroup
+ * @subsys: the subsystem of files to be added
+ * @cfts: array of cftypes to be added
+ * @is_add: whether to add or remove
+ *
+ * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
+ * All @cfts should belong to @subsys.  For removals, this function never
+ * fails.  If addition fails, this function doesn't remove files already
+ * added.  The caller is responsible for cleaning up.
+ */
 static int cgroup_addrm_files(struct cgroup *cgrp, struct cgroup_subsys *subsys,
                              struct cftype cfts[], bool is_add)
 {
        struct cftype *cft;
-       int err, ret = 0;
+       int ret;
+
+       lockdep_assert_held(&cgrp->dentry->d_inode->i_mutex);
+       lockdep_assert_held(&cgroup_mutex);
 
        for (cft = cfts; cft->name[0] != '\0'; cft++) {
                /* does cft->flags tell us to skip this file on @cgrp? */
@@ -2796,16 +2811,17 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cgroup_subsys *subsys,
                        continue;
 
                if (is_add) {
-                       err = cgroup_add_file(cgrp, subsys, cft);
-                       if (err)
+                       ret = cgroup_add_file(cgrp, subsys, cft);
+                       if (ret) {
                                pr_warn("cgroup_addrm_files: failed to add %s, err=%d\n",
-                                       cft->name, err);
-                       ret = err;
+                                       cft->name, ret);
+                               return ret;
+                       }
                } else {
                        cgroup_rm_file(cgrp, cft);
                }
        }
-       return ret;
+       return 0;
 }
 
 static void cgroup_cfts_prepare(void)