linux-kernel - Re: [RFC PATCH 48/86] rcu: handle quiescent states for PREEMPT

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: <87jzpqt7lz.ffs@tglx>
Date:   Thu, 07 Dec 2023 15:22:48 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ankur Arora <ankur.a.arora@...cle.com>, paulmck@...nel.org
Cc:     Ankur Arora <ankur.a.arora@...cle.com>,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        torvalds@...ux-foundation.org, linux-mm@...ck.org, x86@...nel.org,
        akpm@...ux-foundation.org, luto@...nel.org, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        willy@...radead.org, mgorman@...e.de, jon.grimm@....com,
        bharata@....com, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        jgross@...e.com, andrew.cooper3@...rix.com, mingo@...nel.org,
        bristot@...nel.org, mathieu.desnoyers@...icios.com,
        geert@...ux-m68k.org, glaubitz@...sik.fu-berlin.de,
        anton.ivanov@...bridgegreys.com, mattst88@...il.com,
        krypton@...ich-teichert.org, rostedt@...dmis.org,
        David.Laight@...lab.com, richard@....at, mjguzik@...il.com
Subject: Re: [RFC PATCH 48/86] rcu: handle quiescent states for PREEMPT_RCU=n

On Wed, Dec 06 2023 at 17:31, Ankur Arora wrote:
> If we end up needing this, is it valid to just optimistically check if
> a quiescent state needs to be registered (see below)?
> Though this version exposes rcu_data.rcu_urgent_qs outside RCU but maybe
> we can encapsulate that in linux/rcupdate.h.

>  #ifdef CONFIG_PREEMPTION
>  #define preempt_enable() \
>  do { \
>  	barrier(); \
>  	if (unlikely(preempt_count_dec_and_test())) \
>  		__preempt_schedule(); \
> +	else if (unlikely(raw_cpu_read(rcu_data.rcu_urgent_qs))) \
> +		rcu_all_qs_check();

It's still bloat and we can debate this once we come to the conclusion
that the simple forced reschedule is not sufficient. Until then debating
this is just an academic exercise.

Thanks,

        tglx