linux-kernel - IRQF_DISABLED problem

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Date:	Thu, 26 Jul 2007 14:13:56 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Cc:	Linus Torvalds <torvalds@...l.org>
Subject: IRQF_DISABLED problem


I noticed that we only look at the first action in the chain when
determining whether to re-enable local interrupts during handle_IRQ_event.
But we don't try to exclude sharing interrupts with mixtures of
IRQF_DISABLED set and clear.  I just tried to do that locally, and one
of my USB ports disappears, because it shares an interrupt with qla2xxx
which sets IRQF_DISABLED, and UHCI doesn't.

Another possibility is to force it if *any* of the handlers want
IRQF_DISABLED.  This seems to work:

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 203a518..d804a0b 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -308,6 +308,15 @@ int setup_irq(unsigned int irq, struct irqaction *new)
 			goto mismatch;
 #endif
 
+		/* If one handler wants interrupts to be disabled,
+		 * they must all be disabled.  Rather than walk the list of
+		 * handlers twice at interrupt time, just make sure the
+		 * head handler has its flag set
+		 */
+		if ((new->flags & IRQF_DISABLED) &&
+		    !(old->flags & IRQF_DISABLED)
+			old->flags |= IRQF_DISABLED);
+
 		/* add new interrupt at end of irq queue */
 		do {
 			p = &old->next;


This patch makes interrupts requested with IRQF_DISABLED non-matching
fail, in case you think it's a better solution:

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 203a518..2c99b88 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -293,10 +293,12 @@ int setup_irq(unsigned int irq, struct irqaction *new)
 		 * Can't share interrupts unless both agree to and are
 		 * the same type (level, edge, polarity). So both flag
 		 * fields must have IRQF_SHARED set and the bits which
-		 * set the trigger type must match.
+		 * set the trigger type must match and the disabled bit
+		 * must match.
 		 */
 		if (!((old->flags & new->flags) & IRQF_SHARED) ||
-		    ((old->flags ^ new->flags) & IRQF_TRIGGER_MASK)) {
+		    ((old->flags ^ new->flags) &
+		     (IRQF_TRIGGER_MASK | IRQF_DISABLED))) {
 			old_name = old->name;
 			goto mismatch;
 		}

-- 
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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