linux-kernel - Re: [PATCH v5 02/33] genirq: Add irq_alloc_reserved

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Date:	Sun, 23 Feb 2014 00:38:55 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Yinghai Lu <yinghai@...nel.org>
cc:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Tony Luck <tony.luck@...el.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Joerg Roedel <joro@...tes.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v5 02/33] genirq: Add irq_alloc_reserved_desc()

On Sat, 22 Feb 2014, Yinghai Lu wrote:
> On Sat, Feb 22, 2014 at 9:28 AM, Yinghai Lu <yinghai@...nel.org> wrote:
> > On Sat, Feb 22, 2014 at 2:08 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> >>
> >> As I said before irq_reserve_irq() is a misnomer and a
> >> misconception. Of course this needs to be fixed as well.
> >>
> >> And you cannot just blindly change it because !SPARSE can use the
> >> allocation. We are not creating stupid corner cases just to support
> >> your sloppyness. Its not rocket science to do it the right way.
> >>
> >> That said, it might be worthwhile to get rid of the !SPARSE case
> >> completely. That would probably make quite some stuff simpler.
> >
> > So we need to make all arches support SPARSE_IRQ at first?
> >
> > Now we have arm, arm64, c6x, metag, powerpc, sh, x86 support SPARSE_IRQ.
> >
> > The following  are not with SPARSE_IRQ yet:
> > alpha, arc, avr32, blackfin, cris, frv, hexagon, m32r, m68k, microblaze,
> > mips, mn10300, openrisc, parisc, s390, score, sparc, tile, um,
> > unicore32, xtensa.
> 
> or add calling irq_alloc_desc_at() before irq_set_chip... for !SPARSE_IRQ.
> 
> Please check attached partial patch if you like it.

OMG, you really mean that:

+++ b/arch/alpha/kernel/irq_i8259.c
@@ -92,6 +92,7 @@ init_i8259a_irqs(void)
 	outb(0xff, 0xA1);	/* mask all of 8259A-2 */
 
 	for (i = 0; i < 16; i++) {
+		irq_alloc_desc_at(i, 0);
 		irq_set_chip_and_handler(i, &i8259a_irq_type, handle_level_irq);
 	}

You can't be serious about that. There are tons of ways to call into
the core and access an irq descriptor aside of irq_set_chip* before it
is potentially allocated.

Are you going to analyze all of them and add an irq_alloc_desc_at()
before that call?

HELL, NO!

I'm really tired of that.

Stay away from kernel/irq/* and wait for people who are competent
enough and willing to spend the extra thoughts to come up with
solutions which are not completely ass backwards.

Thanks,

	tglx
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