linux-kernel - Re: [PATCH 1/2] itimers: fix racy writes to cpu

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Message-ID: <20090924195732.384bea26@dhcp-lab-109.englab.brq.redhat.com>
Date:	Thu, 24 Sep 2009 19:57:32 +0200
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] itimers: fix racy writes to cpu_itimer fields

On Thu, 24 Sep 2009 16:48:07 +0200
Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> On Thu, 2009-09-24 at 16:35 +0200, Stanislaw Gruszka wrote:
> > incr_error and error fields of struct cpu_itimer are used when calculating
> > next timer tick in check_cpu_itimers() and should not be modified without
> > tsk->sighand->siglock taken.
> 
> Won't it be all-round much better to convert these things to hrtimers
> instead of adding more and more fuzz on top to make them deal with
> jiffies?

Perhaps it would, but I don't know how to do it :{ . Especially how to
precisely account user time. The only idea I have is make something like 
microstate accounting (http://lwn.net/Articles/127296/), but this patch
and whole idea was rejected long time ago. 

Stanislaw
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