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Subject[PATCH] irq, x86: Remove IRQ_DISABLED check in process context IRQ move

As discussed in the thread here
http://marc.info/?l=linux-kernel&m=123964468521142&w=2

On Fri, Apr 10, 2009 at 3:02 PM, Eric W. Biederman
<ebiederm@xmission.com> wrote:
>
> It looks like some additional bugs have slipped in since last I looked.
>
> set_irq_affinity does this:
> ifdef CONFIG_GENERIC_PENDING_IRQ
> if (desc->status & IRQ_MOVE_PCNTXT || desc->status & IRQ_DISABLED) {
> cpumask_copy(desc->affinity, cpumask);
> desc->chip->set_affinity(irq, cpumask);
> } else {
> desc->status |= IRQ_MOVE_PENDING;
> cpumask_copy(desc->pending_mask, cpumask);
> }
> #else
>
> That IRQ_DISABLED case is a software state and as such it has nothing to
> do with how safe it is to move an irq in process context.
>

"Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com> writes:
> On Sat, 2009-04-11 at 04:01 -0700, Eric W. Biederman wrote:
> >
> > If the goal is moving MSIs, we should modify the msi code to be safe
> > in process context and to set IRQ_MOVE_PCNTXT.
> >
> > The only reason we migrate MSIs in interrupt context today is that there
> > wasn't infrastructure for support migration both in interrupt context
> > and outside of it.
>
> Yes. The idea here was to force the MSI migration to happen in process
> context. One of the patches in the series did
>
> disable_irq(dev->irq);
> irq_set_affinity(dev->irq, cpumask_of(dev->cpu));
> enable_irq(dev->irq);
>
> with the above patch adding irq/manage code check for interrupt disabled
> and moving the interrupt in process context.
>
> IIRC, there was no IRQ_MOVE_PCNTXT when we were developing this HPET
> code and we ended up having this ugly hack. IRQ_MOVE_PCNTXT was there
> when we eventually submitted the patch upstream. But, looks like I did a
> blind rebasing instead of using IRQ_MOVE_PCNTXT in hpet MSI code. That
> was my fault. Will send a patch to fix this ugliness.

Below patch fixes this. i.e., revert
commit 932775a4ab622e3c99bd59f14cc7d96722f79501
and add PCNTXT to HPET MSI setup. Also removes copying of desc->affinity
in generic code as set_affinity routines are doing it internally.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
---
arch/x86/kernel/apic/io_apic.c | 2 ++
kernel/irq/manage.c | 5 ++---
2 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 767fe7e..aaf8212 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -3667,12 +3667,14 @@ int arch_setup_hpet_msi(unsigned int irq)
{
int ret;
struct msi_msg msg;
+ struct irq_desc *desc = irq_to_desc(irq);

ret = msi_compose_msg(NULL, irq, &msg);
if (ret < 0)
return ret;

hpet_msi_write(irq, &msg);
+ desc->status |= IRQ_MOVE_PCNTXT;
set_irq_chip_and_handler_name(irq, &hpet_msi_type, handle_edge_irq,
"edge");

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 7e2e7dd..2734eca 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -109,10 +109,9 @@ int irq_set_affinity(unsigned int irq, const struct cpumask *cpumask)
spin_lock_irqsave(&desc->lock, flags);

#ifdef CONFIG_GENERIC_PENDING_IRQ
- if (desc->status & IRQ_MOVE_PCNTXT || desc->status & IRQ_DISABLED) {
- cpumask_copy(desc->affinity, cpumask);
+ if (desc->status & IRQ_MOVE_PCNTXT)
desc->chip->set_affinity(irq, cpumask);
- } else {
+ else {
desc->status |= IRQ_MOVE_PENDING;
cpumask_copy(desc->pending_mask, cpumask);
}
--
1.6.0.6


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