linux-kernel - Re: m68k: [v5] Convert to genirq (WIP)

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Date:	Fri, 2 Sep 2011 19:24:34 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Finn Thain <fthain@...egraphics.com.au>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	"Linux/m68k" <linux-m68k@...r.kernel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: m68k: [v5] Convert to genirq (WIP)

On Fri, Sep 2, 2011 at 14:14, Finn Thain <fthain@...egraphics.com.au> wrote:
> On Sun, 28 Aug 2011, I wrote:
> However, I found another problem. pmac_zilog oopses when its TTY is closed
> (see below). And macsonic does the same when the NIC is closed. The trace
> says that irq_shutdown() died trying to call the chip irq_mask routine,
> when desc->irq_data.chip (in a0) was NULL. Any ideas?

> Unable to handle kernel NULL pointer dereference at virtual address   (null)
> Oops: 00000000
> Modules linked in:
> PC: [<00000000>]   (null)

No, it calls a function pointer that's NULL.

void irq_shutdown(struct irq_desc *desc)
{
        irq_state_set_disabled(desc);
        desc->depth = 1;
        if (desc->irq_data.chip->irq_shutdown)
                desc->irq_data.chip->irq_shutdown(&desc->irq_data);
        if (desc->irq_data.chip->irq_disable)
                desc->irq_data.chip->irq_disable(&desc->irq_data);
        else
                desc->irq_data.chip->irq_mask(&desc->irq_data);
        irq_state_set_masked(desc);
}

Oops, seems I misread the code and assumed the second "if" was an "else if",
as I wrote down in my notes that it calls only one of the 3 functions :-(
But it does need either .irq_disable() or .irq_mask().

The following irq_chip structs have both .irq_disable() and .irq_mask() NULL:
  - arch/m68k/apollo/dn_ints.c:apollo_irq_chip
  - arch/m68k/kernel/ints.c:auto_irq_chip
  - arch/m68k/kernel/ints.c:user_irq_chip

Since this is on Mac and mac_irq_chip is OK, I guess this is a non-PSC Mac,
i.e. the IRQ number is IRQ_MAC_SCC == IRQ_AUTO_4?

Thomas: As we cannot disable or mask autovector interrupts at the
autovector level,
IMHO it doesn't make much sense do add a dummy .irq_mask() function.
Can we add an extra check in irq_shutdown() to not call .irq_mask() if
it's NULL?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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