From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jason Low <jason.low2@hp.com>
Subject: Re: [PATCH v2 1/2] rtmutex Real-Time Linux: Fixing kernel BUG at
 kernel/locking/rtmutex.c:997!
Date: Tue, 07 Apr 2015 12:57:23 -0700
Message-ID: <1428436643.2556.66.camel@j-VirtualBox>
References: <1424395866-81589-1-git-send-email-tmac@hp.com>
	 <1428369962-74723-1-git-send-email-tmac@hp.com>
	 <1428369962-74723-2-git-send-email-tmac@hp.com>
	 <alpine.DEB.2.11.1504071255410.3845@nanos>
	 <1428407236.3152.81.camel@gmail.com>
	 <20150407120403.GN21418@twins.programming.kicks-ass.net>
	 <CAGQ1y=4YNpyztGyPb=rgnBduJfykB8tbG1FQWGEKQWVNeu+nNw@mail.gmail.com>
	 <alpine.DEB.2.11.1504072102510.3845@nanos>
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
Cc: Peter Zijlstra <peterz@infradead.org>,
	Mike Galbraith <umgwanakikbuti@gmail.com>,
	Thavatchai Makphaibulchoke <tmac@hp.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@redhat.com>,
	linux-rt-users <linux-rt-users@vger.kernel.org>,
	jason.low2@hp.com
To: Thomas Gleixner <tglx@linutronix.de>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <alpine.DEB.2.11.1504072102510.3845@nanos>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: linux-rt-users.vger.kernel.org

On Tue, 2015-04-07 at 21:17 +0200, Thomas Gleixner wrote:
> On Tue, 7 Apr 2015, Jason Low wrote:
> > The lock shouldn't be used in get_next_timer_interrupt() either right?
> > 
> > unsigned long get_next_timer_interrupt(unsigned long now)
> > {
> > ...
> > 
> > #ifdef CONFIG_PREEMPT_RT_FULL
> >         /*
> >          * On PREEMPT_RT we cannot sleep here. If the trylock does not
> >          * succeed then we return the worst-case 'expires in 1 tick'
> >          * value.  We use the rt functions here directly to avoid a
> >          * migrate_disable() call.
> >          */
> >         if (!spin_do_trylock(&base->lock))
> >                 return  now + 1;
> > #else
> 
> And how do you protect the walk of the timer wheel against a
> concurrent insertion/removal?

So I just wanted to mention that the issue also applies to
get_next_timer_interrupt(), in addition to run_local_timers(), but if we
really want to remove the lock there, can we always return "now + 1" for
PREEMPT_RT_FULL?