linux-kernel - Re: [RFC 2/2] printk: Add more information about the printk caller

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Date:   Thu, 24 Sep 2020 15:38:50 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     "Ahmed S. Darwish" <a.darwish@...utronix.de>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Prarit Bhargava <prarit@...hat.com>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        Orson Zhai <orsonzhai@...il.com>,
        Changki Kim <changki.kim@...sung.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/2] printk: Add more information about the printk caller

On Thu 2020-09-24 14:53:01, Petr Mladek wrote:
> On Thu 2020-09-24 06:24:14, Ahmed S. Darwish wrote:
> > On Wed, Sep 23, 2020 at 03:56:17PM +0200, Petr Mladek wrote:
> > ...
> > >
> > > -static inline u32 printk_caller_id(void)
> > > +static enum printk_caller_ctx get_printk_caller_ctx(void)
> > > +{
> > > +	if (in_nmi())
> > > +		return printk_ctx_nmi;
> > > +
> > > +	if (in_irq())
> > > +		return printk_ctx_hardirq;
> > > +
> > > +	if (in_softirq())
> > > +		return printk_ctx_softirq;
> > > +
> > > +	return printk_ctx_task;
> > > +}
> > > +
> > 
> > in_softirq() here will be true for both softirq contexts *and*
> > BH-disabled regions. Did you mean in_serving_softirq() instead?
> 
> Good question!
> 
> I am not sure if people would want to distinguish these two
> situations.
> 
> Otherwise, I think that is_softirq() more close to the meaning of
> in_irq(). They both describe a context where a new interrupt has
> to wait until the handling gets enabled again.

Grrrr, I wonder why I thought that in_irq() covered also the situation
when IRQ was disabled. It was likely my wish because disabled
interrupts are problem for printk() because the console might
cause a softlockup.

in_irq() actually behaves like in_serving_softirq().

I am confused and puzzled now. I wonder what contexts are actually
interesting for developers.  It goes back to the ideas from Sergey
about preemption disabled, ...

/me feels shameful and is going to hide under a stone.

Best Regards,
Petr