Subject: Re: 2.6.13-rc6-rt9
From: Thomas Gleixner <tglx@linutronix.de>
Reply-To: tglx@linutronix.de
To: paulmck@us.ibm.com
Cc: George Anzinger <george@mvista.com>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, Ingo Molnar <mingo@elte.hu>,
       linux-kernel@vger.kernel.org, Steven Rostedt <rostdt@goodmis.org>,
       Jeff Dike <jdike@addtoit.com>
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Organization: linutronix
Date: Fri, 30 Sep 2005 08:17:36 +0200
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On Thu, 2005-09-29 at 18:46 -0700, Paul E. McKenney wrote:
> > you are not the culprit :)
> 
> Woo-hoo!!!  Exonerated!!!  This time, anyway...  ;-)

My pleasure :)


> > It can not be run from hardirq context, as it takes a lot of locks
> > (especially our favorites: tasklist_lock and sighand->siglock). :(
> > 
> > Maybe another playground for rcu, but it might also be solved by some
> > other mechanism for accounting and delayed execution in the PREEMPT_RT
> > case.
> 
> Certainly check_thread_timers() and check_process_timers() are playing
> with a number of task_struct fields, so it is not immediately clear
> to me how to safely replace tasklist_lock with RCU, at least not with
> a simple and small patch.
> 
> What did you have in mind for delayed execution?

Do only the time check in hard irq context and defer the lock protected
operations to a softirq context. Have to look deeper at the details
though.

tglx


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