linux-kernel - Re: [PATCH] x86/irq: Use printk_deferred() on raw_spin

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Message-ID: <20200925091934.GW2628@hirez.programming.kicks-ass.net>
Date:   Fri, 25 Sep 2020 11:19:34 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Joe Perches <joe@...ches.com>
Cc:     Daniel Bristot de Oliveira <bristot@...hat.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Marc Zyngier <maz@...nel.org>,
        Peter Xu <peterx@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/irq: Use printk_deferred() on raw_spin_lock()
 protected sections

On Thu, Sep 24, 2020 at 09:08:57AM -0700, Joe Perches wrote:
> On Thu, 2020-09-24 at 12:28 +0200, Peter Zijlstra wrote:
> > On Mon, Sep 21, 2020 at 06:22:12PM +0200, Daniel Bristot de Oliveira wrote:
> > > While testing hotplug I got this BUG:
> > > It was caused by printk() inside a code section protected by a
> > > raw_spin_lock() that ended up calling a serial console that
> > > uses a regular spin_lock().
> > > 
> > > Use the printk_deferred() to avoid calling the serial console
> > > in a raw_spin_lock() protected section.
> > 
> > I consider printk_deferred() to be a bug, can't we just wait for the new
> > printk implementation to land so we don't need all this nonsense?
> 
> It will be good to do a sed fixup for all these
> printk_deferred uses soon,  but in the meantime
> isn't it useful to avoid BUGs?

The kernel isn't PROVE_RAW_LOCK_NESTING clean anyway. Printk is one of
the biggest offenders there anyway, iirc.