linux-kernel - Re: [patch 4/9] oom: Add missing rcu protection of __task_cred() in dump

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Message-Id: <20091210104500.F500.A69D9226@jp.fujitsu.com>
Date:	Thu, 10 Dec 2009 10:57:49 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	kosaki.motohiro@...fujitsu.com,
	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...sign.ru>,
	Al Viro <viro@...iv.linux.org.uk>,
	James Morris <jmorris@...ei.org>,
	David Howells <dhowells@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-mm@...ck.org
Subject: Re: [patch 4/9] oom: Add missing rcu protection of __task_cred() in dump_tasks

> 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@...utronix.de>
> Cc: linux-mm@...ck.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@...fujitsu.com>


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