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

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Message-ID: <13284.1260539371@redhat.com>
Date:	Fri, 11 Dec 2009 13:49:31 +0000
From:	David Howells <dhowells@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	dhowells@...hat.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>,
	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

Thomas Gleixner <tglx@...utronix.de> wrote:

> +		/* 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();

No.  If there's only one access to __task_cred() like this, use
task_cred_xxx() or one of its wrappers instead:

-		       p->pid, __task_cred(p)->uid, p->tgid, mm->total_vm,
+		       p->pid, task_uid(p), p->tgid, mm->total_vm,

that limits the size of the critical section.

David
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