linux-kernel - [PATCH] irq, x86: Remove IRQ_DISABLED check in process context IRQ move

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Date:	Mon, 13 Apr 2009 15:20:58 -0700
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	Gary Hade <garyhade@...ibm.com>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lcm@...ibm.com" <lcm@...ibm.com>, suresh.b.siddha@...el.com
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@...ssion.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@...el.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@...el.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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