linux-kernel - Re: [RFC PATCH v1] pin_on_cpu: Introduce thread CPU pinning system call

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: <1648013936.596672.1579655468604.JavaMail.zimbra@efficios.com>
Date:   Tue, 21 Jan 2020 20:11:08 -0500 (EST)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Chris Lameter <cl@...ux.com>
Cc:     Jann Horn <jannh@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Joel Fernandes <joelaf@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Watson <davejwatson@...com>,
        Will Deacon <will.deacon@....com>, shuah <shuah@...nel.org>,
        Andi Kleen <andi@...stfloor.org>,
        linux-kselftest <linux-kselftest@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Russell King <linux@....linux.org.uk>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Paul <paulmck@...ux.vnet.ibm.com>, Paul Turner <pjt@...gle.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Josh Triplett <josh@...htriplett.org>,
        rostedt <rostedt@...dmis.org>, Ben Maurer <bmaurer@...com>,
        linux-api <linux-api@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>
Subject: Re: [RFC PATCH v1] pin_on_cpu: Introduce thread CPU pinning system
 call

----- On Jan 21, 2020, at 4:44 PM, Chris Lameter cl@...ux.com wrote:

> These scenarios are all pretty complex and will be difficult to understand
> for the user of these APIs.
> 
> I think the easiest solution (and most comprehensible) is for the user
> space process that does per cpu operations to get some sort of signal. If
> its not able to handle that then terminate it. The code makes a basic
> assumption after all that the process is running on a specific cpu. If
> this is no longer the case then its better to abort if the process cannot
> handle moving to a different processor.

The point of pin_on_cpu() is to allow threads to access per-cpu data
structures belonging to a given CPU even if they cannot run on that
CPU (because it is offline).

I am not sure what scenario your signal delivery proposal aims to cover.

Just to try to put this into the context of a specific scenario to see
if I understand your point, is the following what you have in mind ?

1. Thread A issues pin_on_cpu(5),
2. Thread B issues sched_setaffinity removing cpu 5 from thread A's
   affinity mask,
3. Noticing that it would generate an invalid combination, rather than
   failing sched_setaffinity, it would send a SIGSEGV (or other) signal
   to thread A.

Or so you have something entirely different in mind ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com