linux-kernel - Re: [GIT PULL] RCU changes for v5.10

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Date:   Mon, 19 Oct 2020 09:31:43 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] RCU changes for v5.10


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Mon, Oct 12, 2020 at 7:14 AM Ingo Molnar <mingo@...nel.org> wrote:
> >
> > Please pull the latest core/rcu git tree from:
> >
> >    git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git core-rcu-2020-10-12
> 
> I've pulled everything but that last merge and the PREEMPT_COUNT 
> stuff that came with it.
> 
> When Paul asked whether it was ok for RCU to use preempt_count() and 
> I answered in the affirmative, I didn't mean it in the sense of "RCU 
> wants to force it on everybody else too".
>
> I'm pretty convinced that the proper fix is to simply make sure that 
> rcu_free() and friends aren't run under any raw spinlocks. So even 
> if the cost of preempt-count isn't that noticeable, there just isn't 
> a reason for RCU to say "screw everybody else, I want this" when 
> there are other alternatives.

That's certainly true - thanks for catching this & sorting it out from 
the bigger pull request!

Thanks,

	Ingo