From: Frederic Weisbecker <frederic@kernel.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: "Paul E . McKenney" <paulmck@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Uladzislau Rezki <urezki@gmail.com>,
Valentin Schneider <valentin.schneider@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Boqun Feng <boqun.feng@gmail.com>,
Neeraj Upadhyay <neeraju@codeaurora.org>,
Josh Triplett <josh@joshtriplett.org>,
Joel Fernandes <joel@joelfernandes.org>,
rcu@vger.kernel.org
Subject: Re: [PATCH 11/11] rcu/nocb: Don't invoke local rcu core on callback overload from nocb kthread
Date: Mon, 11 Oct 2021 14:11:22 +0200 [thread overview]
Message-ID: <20211011121122.GA356339@lothringen> (raw)
In-Reply-To: <20210930153737.lljjay2cquph7cfv@linutronix.de>
Phew, the last changelog is the most careless...
On Thu, Sep 30, 2021 at 05:37:37PM +0200, Sebastian Andrzej Siewior wrote:
> On 2021-09-30 00:10:12 [+0200], Frederic Weisbecker wrote:
> > rcu_core() tries to ensure that its self-invocation in case of callbacks
> > overload only happen in softirq/rcuc mode. Indeed it doesn't make sense
> > to trigger local RCU core from nocb_cb kthread since it can execute
> > on a CPU different from the target rdp. Also in case of overload, the
> > nocb_cb kthread simply iterates a new loop of callbacks processing.
> >
> > However the "offloaded" check that aims at preventing that is wrong.
> - that?
Rephrasing the changelog:
"However the "offloaded" check that aims at preventing misplaced
rcu_core() invocations is wrong."
>
> > First of all that state is volatile and second: softirq/rcuc can
> > execute while the target rdp is offloaded. As a result rcu_core() can
>
> can what?
"As a result rcu_core() can be invoked on the wrong CPU while in the
process of (de-offloading)."
Thanks!
>
> > Fix that with moving the rcu_core() self-invocation to rcu_core() itself,
> > irrespective of the rdp offloaded state.
>
> Sebastian
next prev parent reply other threads:[~2021-10-11 12:11 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-29 22:10 [PATCH 00/11] rcu: Make rcu_core() safe in PREEMPT_RT with NOCB + a few other fixes Frederic Weisbecker
2021-09-29 22:10 ` [PATCH 01/11] rcu/nocb: Make local rcu_nocb_lock_irqsave() safe against concurrent deoffloading Frederic Weisbecker
2021-09-29 22:10 ` [PATCH 02/11] rcu/nocb: Prepare state machine for a new step Frederic Weisbecker
2021-10-01 17:48 ` Valentin Schneider
2021-10-04 11:35 ` Frederic Weisbecker
2021-09-29 22:10 ` [PATCH 03/11] rcu/nocb: Invoke rcu_core() at the start of deoffloading Frederic Weisbecker
2021-10-01 17:50 ` Valentin Schneider
2021-10-04 12:41 ` Frederic Weisbecker
2021-09-29 22:10 ` [PATCH 04/11] rcu/nocb: Make rcu_core() callbacks acceleration preempt-safe Frederic Weisbecker
2021-10-01 17:50 ` Valentin Schneider
2021-09-29 22:10 ` [PATCH 05/11] rcu/nocb: Make rcu_core() callbacks acceleration (de-)offloading safe Frederic Weisbecker
2021-10-01 17:50 ` Valentin Schneider
2021-10-04 13:14 ` Frederic Weisbecker
2021-09-29 22:10 ` [RFC PATCH 06/11] rcu/nocb: Check a stable offloaded state to manipulate qlen_last_fqs_check Frederic Weisbecker
2021-09-29 22:10 ` [PATCH 07/11] rcu/nocb: Use appropriate rcu_nocb_lock_irqsave() Frederic Weisbecker
2021-10-01 17:50 ` Valentin Schneider
2021-10-04 13:33 ` Frederic Weisbecker
2021-09-29 22:10 ` [PATCH 08/11] rcu/nocb: Limit number of softirq callbacks only on softirq Frederic Weisbecker
2021-10-01 17:51 ` Valentin Schneider
2021-10-04 13:42 ` Frederic Weisbecker
2021-10-05 20:55 ` Paul E. McKenney
2021-09-29 22:10 ` [PATCH 09/11] rcu: Fix callbacks processing time limit retaining cond_resched() Frederic Weisbecker
2021-10-01 17:51 ` Valentin Schneider
2021-09-29 22:10 ` [PATCH 10/11] rcu: Apply callbacks processing time limit only on softirq Frederic Weisbecker
2021-10-01 17:51 ` Valentin Schneider
2021-10-04 13:47 ` Frederic Weisbecker
2021-10-06 15:12 ` Valentin Schneider
2021-10-07 0:18 ` Frederic Weisbecker
2021-09-29 22:10 ` [PATCH 11/11] rcu/nocb: Don't invoke local rcu core on callback overload from nocb kthread Frederic Weisbecker
2021-09-30 15:37 ` Sebastian Andrzej Siewior
2021-10-11 12:11 ` Frederic Weisbecker [this message]
2021-10-01 17:47 ` [PATCH 00/11] rcu: Make rcu_core() safe in PREEMPT_RT with NOCB + a few other fixes Valentin Schneider
2021-10-08 14:03 ` Valentin Schneider
2021-10-08 15:49 ` Paul E. McKenney
2021-10-06 15:13 ` Paul E. McKenney
2021-10-07 8:49 ` Sebastian Andrzej Siewior
2021-10-07 19:12 ` Paul E. McKenney
-- strict thread matches above, loose matches on Subject: below --
2021-10-11 14:51 [PATCH 00/11] rcu: Make rcu_core() safe in PREEMPT_RT with NOCB + a few other fixes v2 Frederic Weisbecker
2021-10-11 14:51 ` [PATCH 11/11] rcu/nocb: Don't invoke local rcu core on callback overload from nocb kthread Frederic Weisbecker
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