linux-kernel - Re: [patch V2 00/29] lockup_detector: Cure hotplug deadlocks and replace duct tape

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Date:   Thu, 14 Sep 2017 07:27:25 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Don Zickus <dzickus@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Nicholas Piggin <npiggin@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Ulrich Obergfell <uobergfe@...hat.com>
Subject: Re: [patch V2 00/29] lockup_detector: Cure hotplug deadlocks and
 replace duct tape


* Don Zickus <dzickus@...hat.com> wrote:

> On Tue, Sep 12, 2017 at 09:36:54PM +0200, Thomas Gleixner wrote:
> > The lockup detector is broken is several ways:
> > 
> >     - It's deadlock prone vs. CPU hotplug in various ways. Some of these
> >       are due to recursive cpus_read_lock() others are due to
> >       cpus_read_lock() from CPU hotplug callbacks which immediately lock
> >       the machine because cpus are write locked.
> > 
> >     - The handling of the cpu hotplug threads happens sideways to the
> >       smpboot thread infrastructure, which is racy and pointless
> > 
> >     - The handling of the user space sysctl interface is a complete
> >       trainwreck as it fiddles directly with variables which can be
> >       modified or evaluated by the running watchdogs.
> > 
> >     - The perf event initialization is a trainwreck as it tries to create
> >       perf events over and over even if perf is not functional (no
> >       hardware, ....). To avoid excessive dmesg spam it contains magic
> >       printk ratelimiting along with either wrong or useless messages.
> > 
> >     - The code structure is horrible as ifdef sections are scattered all
> >       over the place which makes it unreadable
> > 
> >     - There is more wreckage, but see the changelogs for the ugly details.
> >
> 
> Aside from the simple compile issue in patch 25.  I have no issues with this
> patchset.  Thanks Thomas!
> 
> Reviewed-by: Don Zickus <dzickus@...hat.com>

Thanks guys! I've applied the series and will push it out after some testing.

Thanks,

	Ingo