On Tue, 30 Oct 2007 11:26:57 -0500
Russ Anderson <[email protected]> wrote:
> [patch] __do_IRQ does not check IRQ_DISABLED when IRQ_PER_CPU is set
>
> In __do_IRQ(), the normal case is that IRQ_DISABLED is checked and if
> set the handler (handle_IRQ_event()) is not called.
>
> Earlier in __do_IRQ(), if IRQ_PER_CPU is set the code does not check
> IRQ_DISABLED and calls the handler even though IRQ_DISABLED is set.
> This behavior seems unintentional.
>
> One user encountering this behavior is the CPE handler (in
> arch/ia64/kernel/mca.c). When the CPE handler encounters too many
> CPEs (such as a solid single bit error), it sets up a polling timer
> and disables the CPE interrupt (to avoid excessive overhead logging
> the stream of single bit errors). disable_irq_nosync() is called
> which sets IRQ_DISABLED. The IRQ_PER_CPU flag was previously set
> (in ia64_mca_late_init()). The net result is the CPE handler gets
> called even though it is marked disabled.
>
> If the behavior of not checking IRQ_DISABLED when IRQ_PER_CPU is
> set is intentional, it would be worthy of a comment describing
> the intended behavior. disable_irq_nosync() does call chip->disable()
> to provide a chipset specifiec interface for disabling the interrupt,
> which avoids this issue when used.
>
> Comments???
>
It looks right to me.
>
> --------------------------------------------------------------------
> ---
> kernel/irq/handle.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> Index: linus/kernel/irq/handle.c
> ===================================================================
> --- linus.orig/kernel/irq/handle.c 2007-10-30 09:49:26.000000000 -0500
> +++ linus/kernel/irq/handle.c 2007-10-30 10:23:52.436719688 -0500
> @@ -178,9 +178,11 @@ fastcall unsigned int __do_IRQ(unsigned
> */
> if (desc->chip->ack)
> desc->chip->ack(irq);
> - action_ret = handle_IRQ_event(irq, desc->action);
> - if (!noirqdebug)
> - note_interrupt(irq, desc, action_ret);
> + if (likely(!(desc->status & IRQ_DISABLED))) {
> + action_ret = handle_IRQ_event(irq, desc->action);
> + if (!noirqdebug)
> + note_interrupt(irq, desc, action_ret);
> + }
> desc->chip->end(irq);
> return 1;
> }
Alas, I can't remember who wrote (and cares about) the IRQ_PER_CPU support.
Oh well.
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