---

yaml --- r: 289718 b: refs/heads/master c: fb5d2b4 h: refs/heads/master v: v3
git-mirror · Jan 20, 2012 · a5e1e73 · a5e1e73
1 parent e333fe3
commit a5e1e73
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Showing 2 changed files with 8 additions and 4 deletions.
diff --git a/[refs] b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: b78949ebfb563c29808a9d0a772e3adb5561bc80
+refs/heads/master: fb5d2b4cfc24963d0e8a7df57de1ecffa10a04cf
diff --git a/trunk/kernel/cgroup.c b/trunk/kernel/cgroup.c
@@ -2102,10 +2102,14 @@ static int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
 	if (retval)
 		goto out_free_group_list;
 
-	/* prevent changes to the threadgroup list while we take a snapshot. */
-	read_lock(&tasklist_lock);
 	tsk = leader;
 	i = 0;
+	/*
+	 * Prevent freeing of tasks while we take a snapshot. Tasks that are
+	 * already PF_EXITING could be freed from underneath us unless we
+	 * take an rcu_read_lock.
+	 */
+	rcu_read_lock();
 	do {
 		struct task_and_cgroup ent;
 
@@ -2128,11 +2132,11 @@ static int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
 		BUG_ON(retval != 0);
 		i++;
 	} while_each_thread(leader, tsk);
+	rcu_read_unlock();
 	/* remember the number of threads in the array for later. */
 	group_size = i;
 	tset.tc_array = group;
 	tset.tc_array_len = group_size;
-	read_unlock(&tasklist_lock);
 
 	/* methods shouldn't be called if no task is actually migrating */
 	retval = 0;