Comment 6 for bug 1672819

The following seems to fix it, but I need to exercise this a bit more to be 100% certain it is rock solid:

diff --git a/fs/fs_struct.c b/fs/fs_struct.c
index 7dca743..cd7175e2 100644
--- a/fs/fs_struct.c
+++ b/fs/fs_struct.c
@@ -98,8 +98,10 @@ void exit_fs(struct task_struct *tsk)
                int kill;
                task_lock(tsk);
                spin_lock(&fs->lock);
+ rcu_read_lock();
                tsk->fs = NULL;
                kill = !--fs->users;
+ rcu_read_unlock();
                spin_unlock(&fs->lock);
                task_unlock(tsk);
                if (kill)