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-rw-r--r--lib/Makefile2
-rw-r--r--lib/is_single_threaded.c45
2 files changed, 46 insertions, 1 deletions
diff --git a/lib/Makefile b/lib/Makefile
index 7cb65d85aeb..80fe8a3ec12 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -11,7 +11,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
rbtree.o radix-tree.o dump_stack.o \
idr.o int_sqrt.o extable.o prio_tree.o \
sha1.o irq_regs.o reciprocal_div.o argv_split.o \
- proportions.o prio_heap.o ratelimit.o show_mem.o
+ proportions.o prio_heap.o ratelimit.o show_mem.o is_single_threaded.o
lib-$(CONFIG_MMU) += ioremap.o
lib-$(CONFIG_SMP) += cpumask.o
diff --git a/lib/is_single_threaded.c b/lib/is_single_threaded.c
new file mode 100644
index 00000000000..f1ed2fe76c6
--- /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;
+}