2 files changed, 49 insertions, 4 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index f928f2a87b9b..f12ab5c4dec4 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -84,21 +84,21 @@ static cpumask_t cpu_singlethread_map __read_mostly;
 static cpumask_t cpu_populated_map __read_mostly;
 
 /* If it's single threaded, it isn't in the list of workqueues. */
-static inline int is_single_threaded(struct workqueue_struct *wq)
+static inline int is_wq_single_threaded(struct workqueue_struct *wq)
 {
         return wq->singlethread;
 }
 
 static const cpumask_t *wq_cpu_map(struct workqueue_struct *wq)
 {
-        return is_single_threaded(wq)
+        return is_wq_single_threaded(wq)
                 ? &cpu_singlethread_map : &cpu_populated_map;
 }
 
 static
 struct cpu_workqueue_struct *wq_per_cpu(struct workqueue_struct *wq, int cpu)
 {
-        if (unlikely(is_single_threaded(wq)))
+        if (unlikely(is_wq_single_threaded(wq)))
                 cpu = singlethread_cpu;
         return per_cpu_ptr(wq->cpu_wq, cpu);
 }
@@ -769,7 +769,7 @@ static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
 {
         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
         struct workqueue_struct *wq = cwq->wq;
-        const char *fmt = is_single_threaded(wq) ? "%s" : "%s/%d";
+        const char *fmt = is_wq_single_threaded(wq) ? "%s" : "%s/%d";
         struct task_struct *p;
 
         p = kthread_create(worker_thread, cwq, fmt, wq->name, cpu);
diff --git a/lib/is_single_threaded.c b/lib/is_single_threaded.c
new file mode 100644
index 000000000000..f1ed2fe76c65
--- /dev/null
+++ b/lib/is_single_threaded.c
@@ -0,0 +1,45 @@
+/* Function to determine if a thread group is single threaded or not
+ *
+ * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ * - Derived from security/selinux/hooks.c
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/sched.h>
+
+/**
+ * is_single_threaded - Determine if a thread group is single-threaded or not
+ * @p: A task in the thread group in question
+ *
+ * This returns true if the thread group to which a task belongs is single
+ * threaded, false if it is not.
+ */
+bool is_single_threaded(struct task_struct *p)
+{
+        struct task_struct *g, *t;
+        struct mm_struct *mm = p->mm;
+
+        if (atomic_read(&p->signal->count) != 1)
+                goto no;
+
+        if (atomic_read(&p->mm->mm_users) != 1) {
+                read_lock(&tasklist_lock);
+                do_each_thread(g, t) {
+                        if (t->mm == mm && t != p)
+                                goto no_unlock;
+                } while_each_thread(g, t);
+                read_unlock(&tasklist_lock);
+        }
+
+        return true;
+
+no_unlock:
+        read_unlock(&tasklist_lock);
+no:
+        return false;
+}