From: Frederic Weisbecker <frederic@kernel.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
stable@vger.kernel.org
Subject: Re: [RFC PATCH 5/8] entry: Explicitly flush pending rcuog wakeup before last rescheduling points
Date: Mon, 11 Jan 2021 12:50:26 +0100 [thread overview]
Message-ID: <20210111115026.GC242508@lothringen> (raw)
In-Reply-To: <20210111051318.GZ2743@paulmck-ThinkPad-P72>
On Sun, Jan 10, 2021 at 09:13:18PM -0800, Paul E. McKenney wrote:
> On Mon, Jan 11, 2021 at 01:40:14AM +0100, Frederic Weisbecker wrote:
> > On Sat, Jan 09, 2021 at 03:05:33AM +0100, Frederic Weisbecker wrote:
> > > Following the idle loop model, cleanly check for pending rcuog wakeup
> > > before the last rescheduling point on resuming to user mode. This
> > > way we can avoid to do it from rcu_user_enter() with the last resort
> > > self-IPI hack that enforces rescheduling.
> > >
> > > Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> > > Cc: Peter Zijlstra <peterz@infradead.org>
> > > Cc: Thomas Gleixner <tglx@linutronix.de>
> > > Cc: Ingo Molnar<mingo@kernel.org>
> > > Cc: Paul E. McKenney <paulmck@kernel.org>
> > > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > > ---
> > > kernel/entry/common.c | 6 ++++++
> > > kernel/rcu/tree.c | 12 +++++++-----
> > > 2 files changed, 13 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> > > index 378341642f94..8f3292b5f9b7 100644
> > > --- a/kernel/entry/common.c
> > > +++ b/kernel/entry/common.c
> > > @@ -178,6 +178,9 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
> > > /* Architecture specific TIF work */
> > > arch_exit_to_user_mode_work(regs, ti_work);
> > >
> > > + /* Check if any of the above work has queued a deferred wakeup */
> > > + rcu_nocb_flush_deferred_wakeup();
> >
> > So this needs to be moved to the IRQs disabled section, just a few lines later,
> > otherwise preemption may schedule another task that in turn do call_rcu() and create
> > new deferred wake up (thank Paul for the warning). Not to mention moving to
> > another CPU with its own deferred wakeups to flush...
> >
> > I'll fix that for the next version.
>
> Ah, so it was not just my laptop dying, then! ;-)
Note that it fixes the "smp_processor_id() in preemptible" warnings you
reported but it shouldn't fix the other issues.
next prev parent reply other threads:[~2021-01-11 11:51 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-09 2:05 [RFC PATCH 0/8] rcu/sched: Fix ignored rescheduling after rcu_eqs_enter() v3 Frederic Weisbecker
2021-01-09 2:05 ` [RFC PATCH 1/8] rcu: Remove superfluous rdp fetch Frederic Weisbecker
2021-01-09 9:03 ` Greg KH
2021-01-10 10:59 ` Frederic Weisbecker
2021-01-09 2:05 ` [RFC PATCH 2/8] rcu: Pull deferred rcuog wake up to rcu_eqs_enter() callers Frederic Weisbecker
2021-01-09 2:05 ` [RFC PATCH 3/8] rcu/nocb: Perform deferred wake up before last idle's need_resched() check Frederic Weisbecker
2021-01-09 2:05 ` [RFC PATCH 4/8] rcu/nocb: Trigger self-IPI on late deferred wake up before user resume Frederic Weisbecker
2021-01-11 12:04 ` Peter Zijlstra
2021-01-11 12:35 ` Frederic Weisbecker
2021-01-09 2:05 ` [RFC PATCH 5/8] entry: Explicitly flush pending rcuog wakeup before last rescheduling points Frederic Weisbecker
2021-01-11 0:40 ` Frederic Weisbecker
2021-01-11 5:13 ` Paul E. McKenney
2021-01-11 11:50 ` Frederic Weisbecker [this message]
2021-01-11 12:08 ` Peter Zijlstra
2021-01-11 12:54 ` Frederic Weisbecker
2021-01-09 2:05 ` [RFC PATCH 6/8] sched: Report local wake up on resched blind zone within idle loop Frederic Weisbecker
2021-01-11 12:25 ` Peter Zijlstra
2021-01-11 12:56 ` Frederic Weisbecker
2021-01-12 8:24 ` [sched] 9720a64438: WARNING:at_kernel/sched/core.c:#sched_resched_local_assert_allowed kernel test robot
[not found] ` <161062476680.19482.8402362019173198799@build.alporthouse.com>
2021-01-14 15:19 ` [RFC PATCH 6/8] sched: Report local wake up on resched blind zone within idle loop Paul E. McKenney
2021-01-09 2:05 ` [RFC PATCH 7/8] entry: Report local wake up on resched blind zone while resuming to user Frederic Weisbecker
2021-01-13 2:46 ` [entry] 8e01c5f104: unixbench.score -2.2% regression kernel test robot
2021-01-09 2:05 ` [RFC PATCH 8/8] timer: Report ignored local enqueue in nohz mode Frederic Weisbecker
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