From 12a3de0a965826096d8adc593bcf4392a7d5b459 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@tv-sign.ru>
Date: Wed, 30 Apr 2008 00:54:29 -0700
Subject: [PATCH] pids: sys_getpgid: fix unsafe *pid usage, s/tasklist/rcu/

1. sys_getpgid() needs rcu_read_lock() to derive the pgrp _nr, even if
   the task is current, otherwise we can race with another thread which
   does sys_setpgid().

2. Use rcu_read_lock() instead of tasklist_lock when pid != 0, make sure
   that we don't use the NULL pid if the task exits right after successful
   find_task_by_vpid().

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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