Re: [RFC] IRQ handlers run with some high-priority interrupts(not NMI) enabled on some platform

From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Finn Thain <fthain@telegraphics.com.au>
Cc: "Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>,
	Arnd Bergmann <arnd@kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"arnd@arndb.de" <arnd@arndb.de>,
	"geert@linux-m68k.org" <geert@linux-m68k.org>,
	"funaho@jurai.org" <funaho@jurai.org>,
	"philb@gnu.org" <philb@gnu.org>,
	"corbet@lwn.net" <corbet@lwn.net>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"linux-m68k@lists.linux-m68k.org"
	<linux-m68k@lists.linux-m68k.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] IRQ handlers run with some high-priority interrupts(not NMI) enabled on some platform
Date: Mon, 15 Feb 2021 15:06:10 +0200	[thread overview]
Message-ID: <CAHp75VeTKfSAnLUiwJ_SO-r4hUn7aQVTquG0j=k95QO_gk+c1g@mail.gmail.com> (raw)
In-Reply-To: <5fcea94e-6fc9-c340-d7d2-4ae8b69890b8@telegraphics.com.au>

On Sun, Feb 14, 2021 at 7:12 AM Finn Thain <fthain@telegraphics.com.au> wrote:
> On Sat, 13 Feb 2021, Song Bao Hua (Barry Song) wrote:
> > So what is really confusing and a pain to me is that:
> > For years people like me have been writing device drivers
> > with the idea that irq handlers run with interrupts
> > disabled after those commits in genirq. So I don't need
> > to care about if some other IRQs on the same cpu will
> > jump out to access the data the current IRQ handler
> > is accessing.
> >
> > but it turns out the assumption is not true on some platform.
> > So should I start to program devices driver with the new idea
> > interrupts can actually come while irqhandler is running?
> >
> > That's the question which really bothers me.
> >
>
> That scenario seems a little contrived to me (drivers for two or more
> devices sharing state through their interrupt handlers). Is it real?
> I suppose every platform has its quirks. The irq lock in sonic_interrupt()
> is only there because of a platform quirk (the same device can trigger
> either of two IRQs). Anyway, no-one expects all drivers to work on all
> platforms; I don't know why it bothers you so much when platforms differ.

Isn't it any IRQ chip driver which may get IRQ on one or more lines
simultaneously?
The question here is can the handler be re-entrant on the same CPU in that case?

-- 
With Best Regards,
Andy Shevchenko