linux-kernel - Re: [PATCH] lockdep: Avoid triggering hardlockup from debug_show_all

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Date:   Wed, 24 Jan 2018 14:00:35 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Tejun Heo <tj@...nel.org>, Rik van Riel <riel@...com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        kernel-team@...com,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <pmladek@...e.com>
Subject: Re: [PATCH] lockdep: Avoid triggering hardlockup from
 debug_show_all_locks()

On (01/23/18 21:54), Steven Rostedt wrote:
> 
> > Another problem, and I mentioned it somewhere in another email, is that
> > upstream printk people don't receive enough [if any at all] feedback from
> > guys who face printk issues. That's why every time printk_kthread re-surfaces
> > the reaction is "this is not a real problem, no one is seeing printk issues
> > like these, you idiot!". It'd be great to have more "we need ABC, because of
> > XYZ, but printk crashes the system. Here is the backtrace, fix it" reports.
> > As of now, those things mostly are not reported, that's why people are not
> > convinced. Just my 5 cents.
> 
> If you are seeing these issues, have whoever is reporting them to Cc
> LKML, and those of us that would care to listen.

OK. The lack of reports can also signify that we need to change the way we
handle those reports. If we are going to reply "yes, your system crashed
while doing completely innocent printout, but if we fix it then we can
increase by 0.0001% chances of not getting any printouts at all in that
corner case when your system is in recursive double panic over the latest
bitcoin price and your keyboard is on fire" then I don't think people will
care to report anything.

Maybe Tejun will be kind enough to shed some light on how often FB fleet
suffer from printk related issues, or what are the most common scenarios,
etc. [sensitive information can be reported "off list"]

	-ss