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Subject[patch] genirq/MSI: restore __do_IRQ() compat logic temporarily

* Eric W. Biederman <> wrote:

> Ok. Looking at it I almost certain the problem is that
> we lost the hunk of code removed in: 266f0566761cf88906d634727b3d9fc2556f5cbd
> i386: Fix stack switching in do_IRQ
> - if (!irq_desc[irq].handle_irq) {
> - __do_IRQ(irq, regs);
> - goto out_exit;
> - }
> The msi code does not yet set desc->handle_irq. So when we attempt to
> call it we get a NULL pointer dereference.

indeed ... We thought the MSI cleanup went all the way with the irqchips
conversion, that's we suggested to Andrew to drop this chunk in -mm too.

> Except for adding that hunk back in and breaking 4K stacks I don't
> have an immediate fix.

i've attached a bandaid patch for -mm below. Brandon, does this solve
the crash you are seeing?

> I do have a pending cleanup that should result in us setting
> handle_irq in all cases. I will see if I can advance that shortly.

yeah, that's the right solution.


Subject: [patch] genirq/MSI: restore __do_IRQ() compat logic temporarily
From: Ingo Molnar <>

restore the __do_IRQ() compat logic temporarily, until the MSI
genirq conversion has been completed.

disable 4KSTACKS temporarily too.

Signed-off-by: Ingo Molnar <>

arch/i386/Kconfig.debug | 4 ++++
arch/i386/kernel/irq.c | 5 +++++
2 files changed, 9 insertions(+)

Index: linux-2.6.18-rc6-mm1/arch/i386/Kconfig.debug
--- linux-2.6.18-rc6-mm1.orig/arch/i386/Kconfig.debug
+++ linux-2.6.18-rc6-mm1/arch/i386/Kconfig.debug
@@ -56,8 +56,12 @@ config DEBUG_RODATA
portion of the kernel code won't be covered by a 2MB TLB anymore.
If in doubt, say "N".

+# FIXME: Disabled temporarily until the MSI genirq conversion is done!
config 4KSTACKS
bool "Use 4Kb + 4Kb for kernel stacks instead of 8Kb" if DEBUG_KERNEL
+ depends on n
default y
If you say Y here the kernel will use a 4Kb stacksize for the
Index: linux-2.6.18-rc6-mm1/arch/i386/kernel/irq.c
--- linux-2.6.18-rc6-mm1.orig/arch/i386/kernel/irq.c
+++ linux-2.6.18-rc6-mm1/arch/i386/kernel/irq.c
@@ -83,6 +83,10 @@ fastcall unsigned int do_IRQ(struct pt_r

+ if (!irq_desc[irq].handle_irq) {
+ __do_IRQ(irq, regs);
+ goto out_exit;
+ }

curctx = (union irq_ctx *) current_thread_info();
@@ -123,6 +127,7 @@ fastcall unsigned int do_IRQ(struct pt_r
desc->handle_irq(irq, desc, regs);


return 1;
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