From: "Paul E. McKenney" <paulmck@linux.ibm.com>
To: Scott Wood <swood@redhat.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: Thu, 20 Jun 2019 15:25:05 -0700 [thread overview]
Message-ID: <20190620222505.GB26519@linux.ibm.com> (raw)
In-Reply-To: <cf42d8516ac99f69913b1f7a7e8abe578ad27e7f.camel@redhat.com>
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();
Thanx, Paul
next prev parent reply other threads:[~2019-06-20 22:25 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 [this message]
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
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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