pid namespaces: make proc_flush_task() actually from entries from multiple namespaces

This means that proc_flush_task_mnt() is to be called for many proc mounts and
with different ids, depending on the namespace this pid is to be flushed from.
Signed-off-by: NPavel Emelyanov <xemul@openvz.org>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/proc/base.c

@@ -2259,8 +2259,22 @@ static void proc_flush_task_mnt(struct vfsmount *mnt, pid_t pid, pid_t tgid)
 
 void proc_flush_task(struct task_struct *task)
 {
-	proc_flush_task_mnt(proc_mnt, task->pid,
-			thread_group_leader(task) ? 0 : task->tgid);
+	int i, leader;
+	struct pid *pid, *tgid;
+	struct upid *upid;
+
+	leader = thread_group_leader(task);
+	proc_flush_task_mnt(proc_mnt, task->pid, leader ? task->tgid : 0);
+	pid = task_pid(task);
+	if (pid->level == 0)
+		return;
+
+	tgid = task_tgid(task);
+	for (i = 1; i <= pid->level; i++) {
+		upid = &pid->numbers[i];
+		proc_flush_task_mnt(upid->ns->proc_mnt, upid->nr,
+				leader ? 0 : tgid->numbers[i].nr);
+	}
 }
 
 static struct dentry *proc_pid_instantiate(struct inode *dir,