linux-kernel - Re: [PATCH 1/2] break out page allocation warning code

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Date:	Wed, 20 Apr 2011 13:24:26 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	John Stultz <johnstul@...ibm.com>
cc:	Dave Hansen <dave@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
	Michal Nazarewicz <mina86@...a86.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] break out page allocation warning code

On Wed, 20 Apr 2011, KOSAKI Motohiro wrote:

> > That was true a while ago, but you now need to protect every thread's 
> > ->comm with get_task_comm() or ensuring task_lock() is held to protect 
> > against /proc/pid/comm which can change other thread's ->comm.  That was 
> > different before when prctl(PR_SET_NAME) would only operate on current, so 
> > no lock was needed when reading current->comm.
> 
> Right. /proc/pid/comm is evil. We have to fix it. otherwise we need change
> all of current->comm user. It's very lots!
> 

Fixing it in this case would be removing it and only allowing it for 
current via the usual prctl() :)  The code was introduced in 4614a696bd1c 
(procfs: allow threads to rename siblings via /proc/pid/tasks/tid/comm) in 
December 2009 and seems to originally be meant for debugging.  We simply 
can't continue to let it modify any thread's ->comm unless we change the 
over 300 current->comm deferences in the kernel.

I'd prefer that we remove /proc/pid/comm entirely or at least prevent 
writing to it unless CONFIG_EXPERT.
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