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

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Message-ID: <87ee8vlill.mognet@arm.com>
Date:   Fri, 08 Oct 2021 15:03:02 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Frederic Weisbecker <frederic@...nel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Uladzislau Rezki <urezki@...il.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 01/10/21 18:47, Valentin Schneider wrote:
> On 30/09/21 00:10, 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
>>
>> Thanks,
>>       Frederic
>
> FWIW I've had RCU torture with NOCB toggling running for half a day on my
> Arm Juno and nothing to report. I still need to rebase this on an -rt tree
> and give it a spin with CONFIG_PREEMPT_RT.

Rebased on top of v5.15-rc4-rt7-rebase with Thomas' patch reverted and ran
the same thing under CONFIG_PREEMPT_RT, nothing seems to catch on fire, so:

Tested-by: Valentin Schneider <valentin.schneider@....com>