1 files changed, 3 insertions, 0 deletions

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 0b615d62a159..c0e554971df0 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -347,6 +347,8 @@ static int do_task_stat(struct task_struct *task, char * buffer, int whole)
         sigemptyset(&sigign);
         sigemptyset(&sigcatch);
         cutime = cstime = utime = stime = cputime_zero;
+
+        mutex_lock(&tty_mutex);
         read_lock(&tasklist_lock);
         if (task->sighand) {
                 spin_lock_irq(&task->sighand->siglock);
@@ -388,6 +390,7 @@ static int do_task_stat(struct task_struct *task, char * buffer, int whole)
         }
         ppid = pid_alive(task) ? task->group_leader->real_parent->tgid : 0;
         read_unlock(&tasklist_lock);
+        mutex_unlock(&tty_mutex);
 
         if (!whole || num_threads<2)
                 wchan = get_wchan(task);