X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=kernel%2Fcgroup.c;h=e646e870ec5fbe6929e582866c313cd513a5ac0b;hb=e8f1cafd746408478934b9c8b9e9e0d5f450906c;hp=8dc7ec1de42951b0ee27e5691895a7f1c2142f1a;hpb=57114e95e8c4f5035c993fc74bbe94cd9573f1bb;p=firefly-linux-kernel-4.4.55.git

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 8dc7ec1de429..e646e870ec5f 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -91,6 +91,14 @@ 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
@@ -873,7 +881,7 @@ static void cgroup_free_rcu(struct rcu_head *head)
 {
 	struct cgroup *cgrp = container_of(head, struct cgroup, rcu_head);
 
-	schedule_work(&cgrp->free_work);
+	queue_work(cgroup_destroy_wq, &cgrp->free_work);
 }
 
 static void cgroup_diput(struct dentry *dentry, struct inode *inode)
@@ -1995,7 +2003,7 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk,
 
 		/* @tsk either already exited or can't exit until the end */
 		if (tsk->flags & PF_EXITING)
-			continue;
+			goto next;
 
 		/* as per above, nr_threads may decrease, but not increase. */
 		BUG_ON(i >= group_size);
@@ -2003,7 +2011,7 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk,
 		ent.cgrp = task_cgroup_from_root(tsk, root);
 		/* nothing to do if this task is already in the cgroup */
 		if (ent.cgrp == cgrp)
-			continue;
+			goto next;
 		/*
 		 * saying GFP_ATOMIC has no effect here because we did prealloc
 		 * earlier, but it's good form to communicate our expectations.
@@ -2011,7 +2019,7 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk,
 		retval = flex_array_put(group, i, &ent, GFP_ATOMIC);
 		BUG_ON(retval != 0);
 		i++;
-
+	next:
 		if (!threadgroup)
 			break;
 	} while_each_thread(leader, tsk);
@@ -2815,13 +2823,17 @@ static void cgroup_cfts_commit(struct cgroup_subsys *ss,
 {
 	LIST_HEAD(pending);
 	struct cgroup *cgrp, *n;
+	struct super_block *sb = ss->root->sb;
 
 	/* %NULL @cfts indicates abort and don't bother if @ss isn't attached */
-	if (cfts && ss->root != &rootnode) {
+	if (cfts && ss->root != &rootnode &&
+	    atomic_inc_not_zero(&sb->s_active)) {
 		list_for_each_entry(cgrp, &ss->root->allcg_list, allcg_node) {
 			dget(cgrp->dentry);
 			list_add_tail(&cgrp->cft_q_node, &pending);
 		}
+	} else {
+		sb = NULL;
 	}
 
 	mutex_unlock(&cgroup_mutex);
@@ -2844,6 +2856,9 @@ static void cgroup_cfts_commit(struct cgroup_subsys *ss,
 		dput(cgrp->dentry);
 	}
 
+	if (sb)
+		deactivate_super(sb);
+
 	mutex_unlock(&cgroup_cft_mutex);
 }
 
@@ -3772,6 +3787,23 @@ static int cgroup_write_notify_on_release(struct cgroup *cgrp,
 	return 0;
 }
 
+/*
+ * When dput() is called asynchronously, if umount has been done and
+ * then deactivate_super() in cgroup_free_fn() kills the superblock,
+ * there's a small window that vfs will see the root dentry with non-zero
+ * refcnt and trigger BUG().
+ *
+ * That's why we hold a reference before dput() and drop it right after.
+ */
+static void cgroup_dput(struct cgroup *cgrp)
+{
+	struct super_block *sb = cgrp->root->sb;
+
+	atomic_inc(&sb->s_active);
+	dput(cgrp->dentry);
+	deactivate_super(sb);
+}
+
 /*
  * Unregister event and free resources.
  *
@@ -3792,7 +3824,7 @@ static void cgroup_event_remove(struct work_struct *work)
 
 	eventfd_ctx_put(event->eventfd);
 	kfree(event);
-	dput(cgrp->dentry);
+	cgroup_dput(cgrp);
 }
 
 /*
@@ -4077,12 +4109,8 @@ static void css_dput_fn(struct work_struct *work)
 {
 	struct cgroup_subsys_state *css =
 		container_of(work, struct cgroup_subsys_state, dput_work);
-	struct dentry *dentry = css->cgroup->dentry;
-	struct super_block *sb = dentry->d_sb;
 
-	atomic_inc(&sb->s_active);
-	dput(dentry);
-	deactivate_super(sb);
+	cgroup_dput(css->cgroup);
 }
 
 static void init_cgroup_css(struct cgroup_subsys_state *css,
@@ -4712,6 +4740,22 @@ 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
@@ -5022,7 +5066,7 @@ void __css_put(struct cgroup_subsys_state *css)
 
 	v = css_unbias_refcnt(atomic_dec_return(&css->refcnt));
 	if (v == 0)
-		schedule_work(&css->dput_work);
+		queue_work(cgroup_destroy_wq, &css->dput_work);
 }
 EXPORT_SYMBOL_GPL(__css_put);