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SubjectRe: [patch 00/29] lockup_detector: Cure hotplug deadlocks and replace duct tape
On Thu, Aug 31, 2017 at 09:15:58AM +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 steaming pile of duct tape as it
> idiotically 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.
>
> Before I get utterly grumpy, I just pretend that I don't give a sh*t!
>
> The following series sanitizes the facility and addresses the problems.

Hi Thomas,

Thanks for the patchset. I agree with most your issues you complained
about, just wasn't smart enough to figure out the right way to solve them.
Despite your aggressive comments, I will review the code to see if it covers
the scenarios that have popped up over the years and run some testing on my
side. Probably need a few days to do that.

Cheers,
Don

>
> Thanks,
>
> tglx
> ---
> arch/parisc/kernel/process.c | 2
> arch/powerpc/kernel/watchdog.c | 22 -
> arch/x86/events/intel/core.c | 11
> include/linux/nmi.h | 121 +++----
> include/linux/smpboot.h | 4
> kernel/cpu.c | 6
> kernel/smpboot.c | 22 -
> kernel/sysctl.c | 22 -
> kernel/watchdog.c | 638 ++++++++++++++---------------------------
> kernel/watchdog_hld.c | 193 ++++++------
> 10 files changed, 433 insertions(+), 608 deletions(-)
>
>

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