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Message-ID: <20090217194555.GA12091@elte.hu>
Date: Tue, 17 Feb 2009 20:45:55 +0100
From: Ingo Molnar <mingo@...e.hu>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: hpa@...or.com, mingo@...hat.com, tglx@...utronix.de,
linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:irq/genirq] irq: refactor and clean up the free_irq()
code flow
* Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> On Sun, 15 Feb 2009, Ingo Molnar wrote:
> > struct irq_desc *desc = irq_to_desc(irq);
> > - struct irqaction **p;
> > + struct irqaction *action, **p, **pp;
>
> The whole reason for 'pp' seems to be the confusing loop:
>
> > for (;;) {
> > + action = *p;
> > + pp = p;
> > +
> > + if (!action) {
> > + WARN(1, "Trying to free already-free IRQ %d\n", irq);
> > + spin_unlock_irqrestore(&desc->lock, flags);
> > +
> > + return;
> > + }
> >
> > + p = &action->next;
> > + if (action->dev_id != dev_id)
> > + continue;
> >
> > + break;
> > + }
> > + /* Found it - now remove it from the list of entries: */
> > + *pp = action->next;
>
> Where the need for 'pp' would go away if you'd just write it as
>
> if (action->dev_id == dev_id)
> break;
> p = &action->next;
> }
> *p = action->next;
>
> instead. Which also makes it both shorter and more readable.
Ah, good point. I concentrated on an identity transformation
primarily and missed that simplification.
Something like the patch below? (plus the followup cleanup
further below?)
Ingo
------------->
>From 8316e38100c70cd1443ac90074eccdd033aa218d Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@...e.hu>
Date: Tue, 17 Feb 2009 20:28:29 +0100
Subject: [PATCH] irq: further clean up the free_irq() code flow
Linus noticed that the 'pp' variable can be eliminated
altogether, and the loop can be cleaned up further.
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
kernel/irq/manage.c | 11 ++++-------
1 files changed, 4 insertions(+), 7 deletions(-)
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 7a954b8..de5a765 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -575,7 +575,7 @@ int setup_irq(unsigned int irq, struct irqaction *act)
void free_irq(unsigned int irq, void *dev_id)
{
struct irq_desc *desc = irq_to_desc(irq);
- struct irqaction *action, **p, **pp;
+ struct irqaction *action, **p;
unsigned long flags;
WARN(in_interrupt(), "Trying to free IRQ %d from IRQ context!\n", irq);
@@ -592,7 +592,6 @@ void free_irq(unsigned int irq, void *dev_id)
p = &desc->action;
for (;;) {
action = *p;
- pp = p;
if (!action) {
WARN(1, "Trying to free already-free IRQ %d\n", irq);
@@ -601,15 +600,13 @@ void free_irq(unsigned int irq, void *dev_id)
return;
}
+ if (action->dev_id == dev_id)
+ break;
p = &action->next;
- if (action->dev_id != dev_id)
- continue;
-
- break;
}
/* Found it - now remove it from the list of entries: */
- *pp = action->next;
+ *p = action->next;
/* Currently used only by UML, might disappear one day: */
#ifdef CONFIG_IRQ_RELEASE_METHOD
>From f17c75453b2d195eba0a90d9f16a3ba88c85b3b4 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@...e.hu>
Date: Tue, 17 Feb 2009 20:43:37 +0100
Subject: [PATCH] irq: name 'p' variables a bit better
'p' stands for pointer - make it clear in setup_irq() and free_irq()
what kind of pointer it is.
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
kernel/irq/manage.c | 22 +++++++++++-----------
1 files changed, 11 insertions(+), 11 deletions(-)
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index de5a765..c589305 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -399,7 +399,7 @@ int __irq_set_trigger(struct irq_desc *desc, unsigned int irq,
static int
__setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
{
- struct irqaction *old, **p;
+ struct irqaction *old, **old_ptr;
const char *old_name = NULL;
unsigned long flags;
int shared = 0;
@@ -431,8 +431,8 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
* The following block of code has to be executed atomically
*/
spin_lock_irqsave(&desc->lock, flags);
- p = &desc->action;
- old = *p;
+ old_ptr = &desc->action;
+ old = *old_ptr;
if (old) {
/*
* Can't share interrupts unless both agree to and are
@@ -455,8 +455,8 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
/* add new interrupt at end of irq queue */
do {
- p = &old->next;
- old = *p;
+ old_ptr = &old->next;
+ old = *old_ptr;
} while (old);
shared = 1;
}
@@ -507,7 +507,7 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
(int)(new->flags & IRQF_TRIGGER_MASK));
}
- *p = new;
+ *old_ptr = new;
/* Reset broken irq detection when installing new handler */
desc->irq_count = 0;
@@ -575,7 +575,7 @@ int setup_irq(unsigned int irq, struct irqaction *act)
void free_irq(unsigned int irq, void *dev_id)
{
struct irq_desc *desc = irq_to_desc(irq);
- struct irqaction *action, **p;
+ struct irqaction *action, **action_ptr;
unsigned long flags;
WARN(in_interrupt(), "Trying to free IRQ %d from IRQ context!\n", irq);
@@ -589,9 +589,9 @@ void free_irq(unsigned int irq, void *dev_id)
* There can be multiple actions per IRQ descriptor, find the right
* one based on the dev_id:
*/
- p = &desc->action;
+ action_ptr = &desc->action;
for (;;) {
- action = *p;
+ action = *action_ptr;
if (!action) {
WARN(1, "Trying to free already-free IRQ %d\n", irq);
@@ -602,11 +602,11 @@ void free_irq(unsigned int irq, void *dev_id)
if (action->dev_id == dev_id)
break;
- p = &action->next;
+ action_ptr = &action->next;
}
/* Found it - now remove it from the list of entries: */
- *p = action->next;
+ *action_ptr = action->next;
/* Currently used only by UML, might disappear one day: */
#ifdef CONFIG_IRQ_RELEASE_METHOD
--
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