From d4f50e12cbe1bcc23ab01a7daac1d078759bf933 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Thu, 9 Jul 2009 23:28:49 +0200
Subject: [PATCH] --- yaml --- r: 157315 b: refs/heads/master c:
 967cc5371113f9806b39a2ebb2174af2883d96fe h: refs/heads/master i:   157313:
 063608336be098d173a35ae3509a5f92b13ecbbe   157311:
 a73562f22c3563ca81e62962a7d6dfecd007ffc2 v: v3

---
 [refs]                         |  2 +-
 trunk/lib/is_single_threaded.c | 10 ++++++----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/[refs] b/[refs]
index 57ac203ba14f..01cd1d2c9dcd 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 5bb459bb45d1ad3c177485dcf0af01580aa31125
+refs/heads/master: 967cc5371113f9806b39a2ebb2174af2883d96fe
diff --git a/trunk/lib/is_single_threaded.c b/trunk/lib/is_single_threaded.c
index 434010980bdf..bd2bea963364 100644
--- a/trunk/lib/is_single_threaded.c
+++ b/trunk/lib/is_single_threaded.c
@@ -22,8 +22,6 @@ bool current_is_single_threaded(void)
 	struct task_struct *p, *t;
 	bool ret;
 
-	might_sleep();
-
 	if (atomic_read(&task->signal->live) != 1)
 		return false;
 
@@ -31,7 +29,6 @@ bool current_is_single_threaded(void)
 		return true;
 
 	ret = false;
-	down_write(&mm->mmap_sem);
 	rcu_read_lock();
 	for_each_process(p) {
 		if (unlikely(p->flags & PF_KTHREAD))
@@ -45,12 +42,17 @@ bool current_is_single_threaded(void)
 				goto found;
 			if (likely(t->mm))
 				break;
+			/*
+			 * t->mm == NULL. Make sure next_thread/next_task
+			 * will see other CLONE_VM tasks which might be
+			 * forked before exiting.
+			 */
+			smp_rmb();
 		} while_each_thread(p, t);
 	}
 	ret = true;
 found:
 	rcu_read_unlock();
-	up_write(&mm->mmap_sem);
 
 	return ret;
 }