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SubjectPATCH to fix irq sharing and SA_INTERRUPT on x86. please review
further to my email yesterday (to which i've had no response :) i 
propose the attached patch to arch/i386/kernel/irq.c. it corrects what i
see as a bug in interrupt handling.

currently if a driver requests SA_INTERRUPT in an interrupt handler, it
is only called with interrupts disabled if it is the first handler in
the list.

my patch modifies setup_irq to put any interrupt with SA_INTERRUPT in
the front of the handler queue (eg before any handlers without the flag).

and also modifies handle_IRQ_event to only enable interrupts when it
hits the first handler with SA_INTERRUPT not set.

the patch is against 2.5.62 and greatly improves stability on my SMP system.

james

--- linux/arch/i386/kernel/irq.c Wed Feb 12 21:36:34 2003
+++ linux.test/arch/i386/kernel/irq.c Mon Feb 24 21:01:04 2003
@@ -201,11 +201,13 @@
int handle_IRQ_event(unsigned int irq, struct pt_regs * regs, struct irqaction * action)
{
int status = 1; /* Force the "do bottom halves" bit */
-
- if (!(action->flags & SA_INTERRUPT))
- local_irq_enable();
+ int enabled = SA_INTERRUPT;

do {
+ if (~action->flags & enabled) {
+ local_irq_enable();
+ enabled = 0;
+ }
status |= action->flags;
action->handler(irq, action->dev_id, regs);
action = action->next;
@@ -761,23 +763,38 @@
* The following block of code has to be executed atomically
*/
spin_lock_irqsave(&desc->lock,flags);
- p = &desc->action;
- if ((old = *p) != NULL) {
- /* Can't share interrupts unless both agree to */
- if (!(old->flags & new->flags & SA_SHIRQ)) {
- spin_unlock_irqrestore(&desc->lock,flags);
- return -EBUSY;
+ if (new->flags & SA_INTERRUPT) {
+ p = &desc->action;
+ old = *p;
+ /* Add SA_INTERRUPT interrupts to the front of the queue
+ * 'cos it's faster than adding them in the middle */
+ if (old) {
+ if (!(old->flags & new->flags & SA_SHIRQ)) {
+ spin_unlock_irqrestore(&desc->lock,flags);
+ return -EBUSY;
+ }
+ new->next = old;
+ shared = 1;
}
+ *p = new;
+ } else {
+ p = &desc->action;
+ if ((old = *p) != NULL) {
+ /* Can't share interrupts unless both agree to */
+ if (!(old->flags & new->flags & SA_SHIRQ)) {
+ spin_unlock_irqrestore(&desc->lock,flags);
+ return -EBUSY;
+ }

- /* add new interrupt at end of irq queue */
- do {
- p = &old->next;
- old = *p;
- } while (old);
- shared = 1;
+ /* add new interrupt at end of irq queue */
+ do {
+ p = &old->next;
+ old = *p;
+ } while (old);
+ shared = 1;
+ }
+ *p = new;
}
-
- *p = new;

if (!shared) {
desc->depth = 0;
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