1 files changed, 23 insertions, 0 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index d9a8be911f5b..64068667be84 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1648,10 +1648,12 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
                          int flags, const char *unused_dev_name,
                          void *data)
 {
+        struct cgroup_subsys *ss;
         struct cgroup_root *root;
         struct cgroup_sb_opts opts;
         struct dentry *dentry;
         int ret;
+        int i;
         bool new_sb;
 
         /*
@@ -1677,6 +1679,27 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
                 goto out_unlock;
         }
 
+        /*
+         * Destruction of cgroup root is asynchronous, so subsystems may
+         * still be dying after the previous unmount.  Let's drain the
+         * dying subsystems.  We just need to ensure that the ones
+         * unmounted previously finish dying and don't care about new ones
+         * starting.  Testing ref liveliness is good enough.
+         */
+        for_each_subsys(ss, i) {
+                if (!(opts.subsys_mask & (1 << i)) ||
+                    ss->root == &cgrp_dfl_root)
+                        continue;
+
+                if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt)) {
+                        mutex_unlock(&cgroup_mutex);
+                        msleep(10);
+                        ret = restart_syscall();
+                        goto out_free;
+                }
+                cgroup_put(&ss->root->cgrp);
+        }
+
         for_each_root(root) {
                 bool name_match = false;