linux-kernel - Re: [PATCH v2] rcu/nocb: Handle concurrent nocb kthreads creation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20211213190005.GP641268@paulmck-ThinkPad-P17-Gen-1>
Date:   Mon, 13 Dec 2021 11:00:05 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        josh@...htriplett.org, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        joel@...lfernandes.org, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org, urezki@...il.com,
        boqun.feng@...il.com
Subject: Re: [PATCH v2] rcu/nocb: Handle concurrent nocb kthreads creation

On Mon, Dec 13, 2021 at 02:14:07PM +0100, Frederic Weisbecker wrote:
> On Mon, Dec 13, 2021 at 11:28:45AM +0000, David Woodhouse wrote:
> > On Mon, 2021-12-13 at 12:22 +0100, Frederic Weisbecker wrote:
> > > I was about to ack the patch but, should we really add code that isn't going to
> > > be necessary before a long while?
> > 
> > Yeah, I'm torn on that. In this case it's harmless enough and it makes
> > the code reentrant in its own right instead of relying on the fact that
> > the cpuhp code won't invoke it multiple times in parallel. So I think
> > that's reasonable defensive programming.
> 
> The thing is that RCU code is already quite complicated. Are we even at least
> sure that we'll ever make CPU hotplug allow concurrent CPU onlining/offlining?
> 
> This will require much more thoughts and a new hotplug concurrency
> infrastructure that we'll need to base RCU on. IMHO it's a bit early to handle
> that on hotplug individual callbacks.
> 
> But anyway, let's see what Paul thinks about it...

We need to at least think through parallelizing the various RCU
CPU-hotplug notifiers.  For one thing, it might turn out to be necessary
to parallelize those notifiers, perhaps on some non-x86 architecture or
on some non-Amazon .config.  For another thing, doing so might suggest
some simplifications, as has happened in my ongoing rcu_barrier() work.

My thought is to pull in the patches and at the very least leave a
tag recording them for later possible use.

							Thanx, Paul