From: Scott Wood <swood@redhat.com>
To: paulmck@linux.ibm.com
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
Juri Lelli <juri.lelli@redhat.com>,
Clark Williams <williams@redhat.com>,
linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH RT 3/4] rcu: unlock special: Treat irq and preempt disabled the same
Date: Mon, 24 Jun 2019 12:40:19 -0500 [thread overview]
Message-ID: <3deedea922e864ddf6363dc6d0850f42ad33ba50.camel@redhat.com> (raw)
In-Reply-To: <20190622191320.GA23577@linux.ibm.com>
On Sat, 2019-06-22 at 12:13 -0700, Paul E. McKenney wrote:
> On Fri, Jun 21, 2019 at 05:26:06PM -0700, Paul E. McKenney wrote:
> > On Thu, Jun 20, 2019 at 06:08:19PM -0500, Scott Wood wrote:
> > > On Thu, 2019-06-20 at 15:25 -0700, Paul E. McKenney wrote:
> > > > On Thu, Jun 20, 2019 at 04:59:30PM -0500, Scott Wood wrote:
> > > > > On Thu, 2019-06-20 at 14:10 -0700, Paul E. McKenney wrote:
> > > > > > On Tue, Jun 18, 2019 at 08:19:07PM -0500, Scott Wood wrote:
> > > > > > > [Note: Just before posting this I noticed that the
> > > > > > > invoke_rcu_core
> > > > > > > stuff
> > > > > > > is part of the latest RCU pull request, and it has a patch
> > > > > > > that
> > > > > > > addresses this in a more complicated way that appears to deal
> > > > > > > with
> > > > > > > the
> > > > > > > bare irq-disabled sequence as well.
> > > > > >
> > > > > > Far easier to deal with it than to debug the lack of it. ;-)
> > > > > >
> > > > > > > Assuming we need/want to support such sequences, is the
> > > > > > > invoke_rcu_core() call actually going to result in scheduling
> > > > > > > any
> > > > > > > sooner? resched_curr() just does the same setting of
> > > > > > > need_resched
> > > > > > > when it's the same cpu.
> > > > > > > ]
> > > > > >
> > > > > > Yes, invoke_rcu_core() can in some cases invoke the scheduler
> > > > > > sooner.
> > > > > > Setting the CPU-local bits might not have effect until the next
> > > > > > interrupt.
> > > > >
> > > > > Maybe I'm missing something, but I don't see how (in the non-
> > > > > use_softirq
> > > > > case). It just calls wake_up_process(), which in resched_curr()
> > > > > will
> > > > > set
> > > > > need_resched but not do an IPI-to-self.
> > > >
> > > > The common non-rt case will be use_softirq. Or are you referring
> > > > specifically to this block of code in current -rcu?
> > > >
> > > > } else if (exp && irqs_were_disabled && !use_softirq
> > > > &&
> > > > !t-
> > > > >rcu_read_unlock_special.b.deferred_qs) {
> > > > // Safe to awaken and we get no help from
> > > > enabling
> > > > // irqs, unlike bh/preempt.
> > > > invoke_rcu_core();
> > >
> > > Yes, that one. If that block is removed the else path should be
> > > sufficient,
> > > now that an IPI-to-self has been added.
> >
> > I will give it a try and let you know what happens.
>
> How about the following?
Looks good, thanks.
-Scott
next prev parent reply other threads:[~2019-06-24 17:40 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-19 1:19 [PATCH RT 0/4] Address rcutorture issues Scott Wood
2019-06-19 1:19 ` [PATCH RT 1/4] rcu: Acquire RCU lock when disabling BHs Scott Wood
2019-06-20 20:53 ` Paul E. McKenney
2019-06-20 21:06 ` Scott Wood
2019-06-20 21:20 ` Paul E. McKenney
2019-06-20 21:38 ` Scott Wood
2019-06-20 22:16 ` Paul E. McKenney
2019-06-19 1:19 ` [PATCH RT 2/4] sched: migrate_enable: Use sleeping_lock to indicate involuntary sleep Scott Wood
2019-06-19 1:19 ` [RFC PATCH RT 3/4] rcu: unlock special: Treat irq and preempt disabled the same Scott Wood
2019-06-20 21:10 ` Paul E. McKenney
2019-06-20 21:59 ` Scott Wood
2019-06-20 22:25 ` Paul E. McKenney
2019-06-20 23:08 ` Scott Wood
2019-06-22 0:26 ` Paul E. McKenney
2019-06-22 19:13 ` Paul E. McKenney
2019-06-24 17:40 ` Scott Wood [this message]
2019-06-19 1:19 ` [RFC PATCH RT 4/4] rcutorture: Avoid problematic critical section nesting Scott Wood
2019-06-20 21:18 ` Paul E. McKenney
2019-06-20 21:43 ` Scott Wood
2019-06-21 16:38 ` Sebastian Andrzej Siewior
2019-06-21 23:59 ` Paul E. McKenney
2019-06-26 15:08 ` Steven Rostedt
2019-06-26 16:49 ` Scott Wood
2019-06-27 18:00 ` Paul E. McKenney
2019-06-27 20:16 ` Scott Wood
2019-06-27 20:50 ` Paul E. McKenney
2019-06-27 22:46 ` Scott Wood
2019-06-28 0:52 ` Paul E. McKenney
2019-06-28 19:37 ` Scott Wood
2019-06-28 20:24 ` Paul E. McKenney
2019-06-20 19:12 ` [PATCH RT 0/4] Address rcutorture issues Paul E. McKenney
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