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

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Date:	Mon, 25 Apr 2011 13:21:28 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	john stultz <johnstul@...ibm.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	David Rientjes <rientjes@...gle.com>,
	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

> > > I'd prefer that we remove /proc/pid/comm entirely or at least prevent 
> > > writing to it unless CONFIG_EXPERT.
> > 
> > Eeeh. That's probably going to be a tough sell, as I think there is
> > wider interest in what it provides. Its useful for debugging
> > applications not kernels, so I doubt folks will want to rebuild their
> > kernel to try to analyze a java issue.
> > 
> > So I'm well aware that there is the chance that you catch the race and
> > read an incomplete/invalid comm (it was discussed at length when the
> > change went in), but somewhere I've missed how that's causing actual
> > problems. Other then just being "evil" and having the documented race,
> > could you clarify what the issue is that your hitting?
> 
> The problem is, there is no documented as well. Okay, I recognized you
> introduced new locking rule for task->comm. But there is no documented
> it. Thus, We have no way to review current callsites are correct or not.
> Can you please do it? And, I have a question. Do you mean now task->comm
> reader don't need task_lock() even if it is another thread?
> 
> _if_ every task->comm reader have to realize it has a chance to read
> incomplete/invalid comm, task_lock() doesn't makes any help.

ping?



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