linux-kernel - Re: [PATCH -mm] proc: don't take ->siglock for /proc/pid/oom

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Date:	Thu, 1 Apr 2010 01:32:13 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Oleg Nesterov <oleg@...hat.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	anfei <anfei.zhou@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	nishimura@....nes.nec.co.jp,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm] proc: don't take ->siglock for /proc/pid/oom_adj

On Thu, 1 Apr 2010, Oleg Nesterov wrote:

> > That doesn't work for depraceted_mode (sic), you'd need to test for
> > OOM_ADJUST_MIN and OOM_ADJUST_MAX in that case.
> 
> Yes, probably "if (depraceted_mode)" should do more checks, I didn't try
> to verify that MIN/MAX are correctly converted. I showed this code to explain
> what I mean.
> 

Ok, please cc me on the patch, it will be good to get rid of the duplicate 
code and remove oom_adj from struct signal_struct.

> > There have been efforts to reuse as much of this code as possible for
> > other sysctl handlers as well, you might be better off looking for
> 
> David, sorry ;) Right now I'd better try to stop the overloading of
> ->siglock. And, I'd like to shrink struct_signal if possible, but this
> is minor.
> 

Do we need ->siglock?  Why can't we just do

	struct sighand_struct *sighand;
	struct signal_struct *sig;

	rcu_read_lock();
	sighand = rcu_dereference(task->sighand);
	if (!sighand) {
		rcu_read_unlock();
		return;
	}
	sig = task->signal;

	... load/store to sig ...

	rcu_read_unlock();

instead?
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