linux-kernel - Re: [PATCH] rcu: use try_cmpxchg in check_cpu

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <20230301151826.014c5977@gandalf.local.home>
Date:   Wed, 1 Mar 2023 15:18:26 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Uros Bizjak <ubizjak@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH] rcu: use try_cmpxchg in check_cpu_stall

On Wed, 1 Mar 2023 12:08:20 -0800
"Paul E. McKenney" <paulmck@...nel.org> wrote:

> > Attached patch implements this suggestion.  
> 
> Please help me out here.
> 
> Why on earth are we even discussing making this change to code that
> normally never executes?  Performance is not a consideration here.
> 
> What am I missing here?  Is there some sort of forward-progress
> issue that this change addresses?

Well, we sorta hijacked this thread. It turned into a more general
discussion, as there is code that this change will be useful for
(ring_buffer.c), but we just happen to be having the discussion here.

Where it will at most remove some text and give you back a few extra bytes
of memory ;-)

But if we do use cmpxchg_success() IMHO, it does improve readability.

> -	    cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
> +	    cmpxchg_success(&rcu_state.jiffies_stall, js, jn)) {

-- Steve