1 files changed, 36 insertions, 26 deletions

diff --git a/lib/is_single_threaded.c b/lib/is_single_threaded.c
index f1ed2fe76c65..2762516e0a5e 100644
--- a/lib/is_single_threaded.c
+++ b/lib/is_single_threaded.c
@@ -12,34 +12,44 @@
 
 #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.
+/*
+ * Returns true if the task does not share ->mm with another thread/process.
  */
-bool is_single_threaded(struct task_struct *p)
+bool is_single_threaded(struct task_struct *task)
 {
-        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);
-        }
+        struct mm_struct *mm = task->mm;
+        struct task_struct *p, *t;
+        bool ret;
+
+        might_sleep();
+
+        if (atomic_read(&task->signal->live) != 1)
+                return false;
 
-        return true;
+        if (atomic_read(&mm->mm_users) == 1)
+                return true;
+
+        ret = false;
+        down_write(&mm->mmap_sem);
+        rcu_read_lock();
+        for_each_process(p) {
+                if (unlikely(p->flags & PF_KTHREAD))
+                        continue;
+                if (unlikely(p == task->group_leader))
+                        continue;
+
+                t = p;
+                do {
+                        if (unlikely(t->mm == mm))
+                                goto found;
+                        if (likely(t->mm))
+                                break;
+                } while_each_thread(p, t);
+        }
+        ret = true;
+found:
+        rcu_read_unlock();
+        up_write(&mm->mmap_sem);
 
-no_unlock:
-        read_unlock(&tasklist_lock);
-no:
-        return false;
+        return ret;
 }