1 files changed, 19 insertions, 3 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f9c99abc38ab..e801ecfa36ef 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1086,6 +1086,12 @@ static int rebind_subsystems(struct cgroupfs_root *root,
                 }
         }
 
+        /*
+         * Mark @root has finished binding subsystems.  @root->subsys_mask
+         * now matches the bound subsystems.
+         */
+        root->flags |= CGRP_ROOT_SUBSYS_BOUND;
+
         return 0;
 }
 
@@ -1485,6 +1491,14 @@ static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
 
         init_cgroup_root(root);
 
+        /*
+         * We need to set @root->subsys_mask now so that @root can be
+         * matched by cgroup_test_super() before it finishes
+         * initialization; otherwise, competing mounts with the same
+         * options may try to bind the same subsystems instead of waiting
+         * for the first one leading to unexpected mount errors.
+         * SUBSYS_BOUND will be set once actual binding is complete.
+         */
         root->subsys_mask = opts->subsys_mask;
         root->flags = opts->flags;
         ida_init(&root->cgroup_ida);
@@ -1734,9 +1748,11 @@ static void cgroup_kill_sb(struct super_block *sb) {
         mutex_lock(&cgroup_root_mutex);
 
         /* Rebind all subsystems back to the default hierarchy */
-        ret = rebind_subsystems(root, 0, root->subsys_mask);
-        /* Shouldn't be able to fail ... */
-        BUG_ON(ret);
+        if (root->flags & CGRP_ROOT_SUBSYS_BOUND) {
+                ret = rebind_subsystems(root, 0, root->subsys_mask);
+                /* Shouldn't be able to fail ... */
+                BUG_ON(ret);
+        }
 
         /*
          * Release all the links from cset_links to this hierarchy's