[PATCH] cpuset: fix cpuset_print_task_mems_allowed() vs rename() race

[Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>]

rename() will change dentry->d_name. The result of this race can
be worse than seeing partially rewritten name, but we might access
a stale pointer because rename() will re-allocate memory to hold
a longer name.

It's safe in the protection of dentry->d_lock.

Signed-off-by: Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
---
 kernel/cpuset.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 16be7c9..b2476c2 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2606,8 +2606,12 @@ void cpuset_print_task_mems_allowed(struct task_struct *tsk)
 
 	dentry = task_cs(tsk)->css.cgroup->dentry;
 	spin_lock(&cpuset_buffer_lock);
+
+	spin_lock(&dentry->d_lock);
 	snprintf(cpuset_name, CPUSET_NAME_LEN,
 		 dentry ? (const char *)dentry->d_name.name : "/");
+	spin_unlock(&dentry->d_lock);
+
 	nodelist_scnprintf(cpuset_nodelist, CPUSET_NODELIST_LEN,
 			   tsk->mems_allowed);
 	printk(KERN_INFO "%s cpuset=%s mems_allowed=%s\n",
-- 
1.8.0.2