1 files changed, 27 insertions, 3 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 4c62513fe19f..a7b98ee35ef7 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -90,6 +90,14 @@ static DEFINE_MUTEX(cgroup_mutex);
 static DEFINE_MUTEX(cgroup_root_mutex);
 
 /*
+ * cgroup destruction makes heavy use of work items and there can be a lot
+ * of concurrent destructions.  Use a separate workqueue so that cgroup
+ * destruction work items don't end up filling up max_active of system_wq
+ * which may lead to deadlock.
+ */
+static struct workqueue_struct *cgroup_destroy_wq;
+
+/*
  * Generate an array of cgroup subsystem pointers. At boot time, this is
  * populated with the built in subsystems, and modular subsystems are
  * registered after that. The mutable section of this array is protected by
@@ -871,7 +879,7 @@ static void cgroup_free_rcu(struct rcu_head *head)
         struct cgroup *cgrp = container_of(head, struct cgroup, rcu_head);
 
         INIT_WORK(&cgrp->destroy_work, cgroup_free_fn);
-        schedule_work(&cgrp->destroy_work);
+        queue_work(cgroup_destroy_wq, &cgrp->destroy_work);
 }
 
 static void cgroup_diput(struct dentry *dentry, struct inode *inode)
@@ -4249,7 +4257,7 @@ static void css_free_rcu_fn(struct rcu_head *rcu_head)
          * css_put().  dput() requires process context which we don't have.
          */
         INIT_WORK(&css->destroy_work, css_free_work_fn);
-        schedule_work(&css->destroy_work);
+        queue_work(cgroup_destroy_wq, &css->destroy_work);
 }
 
 static void css_release(struct percpu_ref *ref)
@@ -4539,7 +4547,7 @@ static void css_killed_ref_fn(struct percpu_ref *ref)
                 container_of(ref, struct cgroup_subsys_state, refcnt);
 
         INIT_WORK(&css->destroy_work, css_killed_work_fn);
-        schedule_work(&css->destroy_work);
+        queue_work(cgroup_destroy_wq, &css->destroy_work);
 }
 
 /**
@@ -5063,6 +5071,22 @@ out:
         return err;
 }
 
+static int __init cgroup_wq_init(void)
+{
+        /*
+         * There isn't much point in executing destruction path in
+         * parallel.  Good chunk is serialized with cgroup_mutex anyway.
+         * Use 1 for @max_active.
+         *
+         * We would prefer to do this in cgroup_init() above, but that
+         * is called before init_workqueues(): so leave this until after.
+         */
+        cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
+        BUG_ON(!cgroup_destroy_wq);
+        return 0;
+}
+core_initcall(cgroup_wq_init);
+
 /*
  * proc_cgroup_show()
  *  - Print task's cgroup paths into seq_file, one line for each hierarchy