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

[Ingo Molnar <mingo@elte.hu>]

* Eric W. Biederman <ebiederm@xmission.com> 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.

	Ingo

------------------>
Subject: [patch] genirq/MSI: restore __do_IRQ() compat logic temporarily
From: Ingo Molnar <mingo@elte.hu>

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

disable 4KSTACKS temporarily too.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
 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
 	help
 	  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
 	}
 #endif
 
+	if (!irq_desc[irq].handle_irq) {
+		__do_IRQ(irq, regs);
+		goto out_exit;
+	}
 #ifdef CONFIG_4KSTACKS
 
 	curctx = (union irq_ctx *) current_thread_info();
@@ -123,6 +127,7 @@ fastcall unsigned int do_IRQ(struct pt_r
 #endif
 		desc->handle_irq(irq, desc, regs);
 
+out_exit:
 	irq_exit();
 
 	return 1;