Subject: Re: [PATCH 1/2] break out page allocation warning code
From: Dave Hansen <dave@linux.vnet.ibm.com>
To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Johannes Weiner <hannes@cmpxchg.org>,
        Michal Nazarewicz <mina86@mina86.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        John Stultz <johnstul@us.ibm.com>
In-Reply-To: <20110420112006.461A.A69D9226@jp.fujitsu.com>
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	 <20110420105059.460C.A69D9226@jp.fujitsu.com>
	 <20110420112006.461A.A69D9226@jp.fujitsu.com>
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Date: Tue, 19 Apr 2011 19:46:02 -0700
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On Wed, 2011-04-20 at 11:19 +0900, KOSAKI Motohiro wrote:
> > +     memcpy(tmp_comm, tsk->comm_buf, TASK_COMM_LEN);
> > +     tsk->comm = tmp;
> >       /*
> > -      * Threads may access current->comm without holding
> > -      * the task lock, so write the string carefully.
> > -      * Readers without a lock may see incomplete new
> > -      * names but are safe from non-terminating string reads.
> > +      * Make sure no one is still looking at tsk->comm_buf
> >        */
> > -     memset(tsk->comm, 0, TASK_COMM_LEN);
> > -     wmb();
> > -     strlcpy(tsk->comm, buf, sizeof(tsk->comm));
> > +     synchronize_rcu();
> 
> The doc says,
> 
> /**
>  * synchronize_rcu - wait until a grace period has elapsed.

Yeah, yeah... see "completely untested". :)

I'll see if dropping the locks or something else equally hackish can
help.  

-- Dave

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