linux-kernel - Re: [PATCH 00/11] rcu: Make rcu_core() safe in PREEMPT

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Date:   Wed, 6 Oct 2021 08:13:39 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Boqun Feng <boqun.feng@...il.com>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Josh Triplett <josh@...htriplett.org>,
        Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org
Subject: Re: [PATCH 00/11] rcu: Make rcu_core() safe in PREEMPT_RT with NOCB
 + a few other fixes

On Thu, Sep 30, 2021 at 12:10:01AM +0200, Frederic Weisbecker wrote:
> PREEMPT_RT has made rcu_core() preemptible, making it unsafe against
> concurrent NOCB (de-)offloading.
> 
> Thomas suggested to drop the local_lock() based solution and simply
> check the offloaded state while context looks safe but that's not
> enough. Here is a bit of rework.
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> 	rcu/rt
> 
> HEAD: aac1c58961446c731f2e989bd822ca1fd2659bad

Many of these look quite good, but any chance of getting an official
Tested-by from someone in the -rt community?

							Thanx, Paul

> Thanks,
> 	Frederic
> ---
> 
> Frederic Weisbecker (10):
>       rcu/nocb: Make local rcu_nocb_lock_irqsave() safe against concurrent deoffloading
>       rcu/nocb: Prepare state machine for a new step
>       rcu/nocb: Invoke rcu_core() at the start of deoffloading
>       rcu/nocb: Make rcu_core() callbacks acceleration (de-)offloading safe
>       rcu/nocb: Check a stable offloaded state to manipulate qlen_last_fqs_check
>       rcu/nocb: Use appropriate rcu_nocb_lock_irqsave()
>       rcu/nocb: Limit number of softirq callbacks only on softirq
>       rcu: Fix callbacks processing time limit retaining cond_resched()
>       rcu: Apply callbacks processing time limit only on softirq
>       rcu/nocb: Don't invoke local rcu core on callback overload from nocb kthread
> 
> Thomas Gleixner (1):
>       rcu/nocb: Make rcu_core() callbacks acceleration preempt-safe
> 
> 
>  include/linux/rcu_segcblist.h | 51 +++++++++++++++++++-------
>  kernel/rcu/rcu_segcblist.c    | 10 ++---
>  kernel/rcu/rcu_segcblist.h    |  7 ++--
>  kernel/rcu/tree.c             | 85 ++++++++++++++++++++++++++++++-------------
>  kernel/rcu/tree.h             | 16 +++++---
>  kernel/rcu/tree_nocb.h        | 29 ++++++++++++---
>  6 files changed, 136 insertions(+), 62 deletions(-)