linux-kernel - Re: [PATCH RFC] tracepoint: Introduce tracepoint callbacks executing with preempt on

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]

Date:   Fri, 27 Apr 2018 11:42:15 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     rostedt <rostedt@...dmis.org>
Cc:     Joel Fernandes <joelaf@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Boqun Feng <boqun.feng@...il.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        fweisbec <fweisbec@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        kbuild test robot <fengguang.wu@...el.com>,
        baohong liu <baohong.liu@...el.com>,
        vedang patel <vedang.patel@...el.com>,
        kernel-team <kernel-team@...roid.com>
Subject: Re: [PATCH RFC] tracepoint: Introduce tracepoint callbacks
 executing with preempt on

----- On Apr 27, 2018, at 10:47 AM, rostedt rostedt@...dmis.org wrote:

> On Fri, 27 Apr 2018 10:26:29 -0400 (EDT)
> Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:
> 
>> The general approach and the implementation look fine, except for
>> one small detail: I would be tempted to explicitly disable preemption
>> around the call to the tracepoint callback for the rcuidle variant,
>> unless we plan to audit every tracer right away to remove any assumption
>> that preemption is disabled in the callback implementation.
> 
> I'm thinking that we do that audit. There shouldn't be many instances
> of it. I like the idea that a tracepoint callback gets called with
> preemption enabled.

I see that ftrace explicitly disables preemption in its ring buffer
code. FWIW, this is redundant when called from sched-rcu tracepoints
and from kprobes which adds unnecessary performance overhead.

LTTng expects preemption to be disabled when invoked. I can adapt on my
side as needed, but would prefer not to have redundant preemption disabling
for probes hooking on sched-rcu tracepoints (which is the common case).

Do perf callbacks expect preemption to be disabled ?

Thanks,

Mathieu

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