Merge branch 'for-3.13-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup fixes from Tejun Heo:
 "Fixes for three issues.

   - cgroup destruction path could swamp system_wq possibly leading to
     deadlock.  This actually seems to happen in the wild with memcg
     because memcg destruction path adds nested dependency on system_wq.

     Resolved by isolating cgroup destruction work items on its
     dedicated workqueue.

   - Possible locking context deadlock through seqcount reported by
     lockdep

   - Memory leak under certain conditions"

* 'for-3.13-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: fix cgroup_subsys_state leak for seq_files
  cpuset: Fix memory allocator deadlock
  cgroup: use a dedicated workqueue for cgroup destruction

2 files changed, 37 insertions, 6 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 4c62513fe19f..8b729c278b64 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
@@ -191,6 +199,7 @@ static void cgroup_destroy_css_killed(struct cgroup *cgrp);
 static int cgroup_destroy_locked(struct cgroup *cgrp);
 static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
                               bool is_add);
+static int cgroup_file_release(struct inode *inode, struct file *file);
 
 /**
  * cgroup_css - obtain a cgroup's css for the specified subsystem
@@ -871,7 +880,7 @@ 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)
@@ -2421,7 +2430,7 @@ static const struct file_operations cgroup_seqfile_operations = {
         .read = seq_read,
         .write = cgroup_file_write,
         .llseek = seq_lseek,
-        .release = single_release,
+        .release = cgroup_file_release,
 };
 
 static int cgroup_file_open(struct inode *inode, struct file *file)
@@ -2482,6 +2491,8 @@ static int cgroup_file_release(struct inode *inode, struct file *file)
                 ret = cft->release(inode, file);
         if (css->ss)
                 css_put(css);
+        if (file->f_op == &cgroup_seqfile_operations)
+                single_release(inode, file);
         return ret;
 }
 
@@ -4249,7 +4260,7 @@ 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 +4550,7 @@ 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 +5074,22 @@ 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
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 6bf981e13c43..4772034b4b17 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1033,8 +1033,10 @@ static void cpuset_change_task_nodemask(struct task_struct *tsk,
         need_loop = task_has_mempolicy(tsk) ||
                         !nodes_intersects(*newmems, tsk->mems_allowed);
 
-        if (need_loop)
+        if (need_loop) {
+                local_irq_disable();
                 write_seqcount_begin(&tsk->mems_allowed_seq);
+        }
 
         nodes_or(tsk->mems_allowed, tsk->mems_allowed, *newmems);
         mpol_rebind_task(tsk, newmems, MPOL_REBIND_STEP1);
@@ -1042,8 +1044,10 @@ static void cpuset_change_task_nodemask(struct task_struct *tsk,
         mpol_rebind_task(tsk, newmems, MPOL_REBIND_STEP2);
         tsk->mems_allowed = *newmems;
 
-        if (need_loop)
+        if (need_loop) {
                 write_seqcount_end(&tsk->mems_allowed_seq);
+                local_irq_enable();
+        }
 
         task_unlock(tsk);
 }