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  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:   Tue, 7 Aug 2018 18:17:42 -0700
From:   Joel Fernandes <>
To:     Steven Rostedt <>
Cc:     Joel Fernandes <>,
        LKML <>,
        "Cc: Android Kernel" <>,
        Boqun Feng <>,
        Byungchul Park <>,
        Ingo Molnar <>,
        Masami Hiramatsu <>,
        Mathieu Desnoyers <>,
        Namhyung Kim <>,
        Paul McKenney <>,
        Peter Zijlstra <>,
        Thomas Glexiner <>,
        Tom Zanussi <>
Subject: Re: [PATCH v12 3/3] tracing: Centralize preemptirq tracepoints and
 unify their usage

On Tue, Aug 7, 2018 at 5:48 PM, Steven Rostedt <> wrote:
> On Tue, 07 Aug 2018 19:54:13 -0400
> Joel Fernandes <> wrote:
>> >OK, I hit this bug, but it's not because of the partial revert. This
>> >bug seems it needs to be another partial revert. I like you movement of
>> >the code, but I'm starting to doubt that we can use a trace event as a
>> >hook for critical areas yet. Well, not until we can use srcu in NMI.
>> >
>> I sent a patch to use srcu for all tracepoints including nmi. That
>> patch also removes this warning and fixes the one other issue masami
>> reported (hot plug causing a warning).
> Is it one I can take, or does Paul have it? I'll need it to continue
> with this as is, because I can't pass my tests without triggering that
> warning (and that fails the test).

I think you could take it if you're Ok with it, its purely in the
tracing code and I tested it yesterday morning. Its attached to this
email. I tested that it fixes the mmio trace (hotplug related) issue..

>> If Paul and Mathieu can confirm SRCU works on offline CPUs that would
>> be great.
> Yes please.

BTW I found this in Paul's docs RCU Requirements docs, "SRCU is insensitive
to whether or not a CPU is online" so I think it will work.

The paragraph was..
Also unlike other RCU flavors, SRCU's callbacks-wait function
srcu_barrier() may be invoked from CPU-hotplug notifiers,
though this is not necessarily a good idea.
The reason that this is possible is that SRCU is insensitive
to whether or not a CPU is online, which means that srcu_barrier()
need not exclude CPU-hotplug operations.

>> It's just this one warning or anything else that makes you feel
>> tracepoints for critical paths isn't feasible?
> Currently I'm down to this, but I can't get past my first test in my
> ktest suite, because it fails here.

Ok hopefully this will get you past that. Sorry for the frustration.

View attachment "0001-tracepoint-Run-tracepoints-even-after-CPU-is-offline.patch" of type "text/x-patch" (6127 bytes)

Powered by blists - more mailing lists