linux-kernel - Re: sched: serial port lockdep warning when offlining CPUs

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Message-ID: <20170928120532.cjidduvjj5xygaid@hirez.programming.kicks-ass.net>
Date:   Thu, 28 Sep 2017 14:05:32 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sasha Levin <levinsasha928@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        "pmladek@...e.com" <pmladek@...e.com>,
        "sergey.senozhatsky@...il.com" <sergey.senozhatsky@...il.com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>
Subject: Re: sched: serial port lockdep warning when offlining CPUs

(please linewrap normal text at 72 chars)

On Thu, Sep 28, 2017 at 11:45:30AM +0000, Levin, Alexander (Sasha Levin) wrote:
> Okay, that seems to have delt with the callbacks supressed issue.
> 
> I also seem to be hitting it as a result of the scheduler triggering a
> WARN, where print_stack_trace(), for example, just uses printk().
> 
> Now I'm not sure what's your approach here, do we keep converting
> printk to printk_deferred one by one until we whacked every mole?

Nah.. WARN's _should_ not trigger. If they do we fix that.

Getting a lockdep splat after a WARN is something I can live with.

And you really don't want that deferred nonsense for WARNs, because that
means you'll risk not over getting the output.