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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [patch 4/9] oom: Add missing rcu protection of __task_cred() in dump_tasks
Cc: kosaki.motohiro@jp.fujitsu.com, LKML <linux-kernel@vger.kernel.org>,
       "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
       Dipankar Sarma <dipankar@in.ibm.com>, Ingo Molnar <mingo@elte.hu>,
       Peter Zijlstra <peterz@infradead.org>, Oleg Nesterov <oleg@tv-sign.ru>,
       Al Viro <viro@zeniv.linux.org.uk>, James Morris <jmorris@namei.org>,
       David Howells <dhowells@redhat.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linus Torvalds <torvalds@linux-foundation.org>, linux-mm@kvack.org
In-Reply-To: <20091210004703.148689096@linutronix.de>
References: <20091210001308.247025548@linutronix.de> <20091210004703.148689096@linutronix.de>
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Date: Thu, 10 Dec 2009 10:57:49 +0900 (JST)
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> dump_tasks accesses __task_cred() without being in a RCU read side
> critical section. tasklist_lock is not protecting that when
> CONFIG_TREE_PREEMPT_RCU=y.
> 
> Add a rcu_read_lock/unlock() section around the code which accesses
> __task_cred().
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: linux-mm@kvack.org
> ---
>  mm/oom_kill.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> Index: linux-2.6-tip/mm/oom_kill.c
> ===================================================================
> --- linux-2.6-tip.orig/mm/oom_kill.c
> +++ linux-2.6-tip/mm/oom_kill.c
> @@ -329,10 +329,13 @@ static void dump_tasks(const struct mem_
>  			task_unlock(p);
>  			continue;
>  		}
> +		/* Protect __task_cred() access */
> +		rcu_read_lock();
>  		printk(KERN_INFO "[%5d] %5d %5d %8lu %8lu %3d     %3d %s\n",
>  		       p->pid, __task_cred(p)->uid, p->tgid, mm->total_vm,
>  		       get_mm_rss(mm), (int)task_cpu(p), p->signal->oom_adj,
>  		       p->comm);
> +		rcu_read_unlock();
>  		task_unlock(p);
>  	} while_each_thread(g, p);
>  }

Looks straight forward and correct to me.

	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>