linux-kernel - Re: [PATCH 2/2 v3] lib: debugobjects: touch watchdog to avoid softlockup when !CONFIG

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Date:   Thu, 18 Jan 2018 16:15:12 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Yang Shi <yang.s@...baba-inc.com>, longman@...hat.com,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2 v3] lib: debugobjects: touch watchdog to avoid
 softlockup when !CONFIG_PREEMPT

On Thu, 18 Jan 2018, Peter Zijlstra wrote:

> On Thu, Jan 18, 2018 at 10:02:25AM +0100, Thomas Gleixner wrote:
> > > >   2) We can do a cond_resched() if not in atomic context and interrupts are
> > > >      enabled.
> > > 
> > > I did try this before I went with touching softlockup watchdog approach. The
> > > problem is in_atomic() can't tell if it is in atomic context on non-preempt
> > > kernel. For preempt kernel, it is easy.
> > 
> > Peter, can we do anything about that?
> 
> Not really :/ Take for instance a spinlock on !PREEMPT, only the lock
> variable is touched, preempt_count isn't. So we cannot know.

Fair enough.