Acknowledge IRQ *before* calling the handler

5da1aea7ab3c ("Acknoledge interrupt after handler call") moved the IRQ ack
to after calling the handler because of overflows. But that was because the
interrupts were getting enabled at some point. Now that all spl levels
above 0 just disable interrupts, once we have called spl7 we are safe
until splx_cli is called (and even that doesn't release interrupts, only
the eventual iret will).

And if the handler triggers another IRQ, it will be lost, so we do want
to ack the IRQ before handling it.

1 files changed, 27 insertions, 25 deletions

diff --git a/i386/i386at/interrupt.S b/i386/i386at/interrupt.S
index 1f661f8d..e9e9c0ef 100644
--- a/i386/i386at/interrupt.S
+++ b/i386/i386at/interrupt.S
@@ -41,38 +41,19 @@
 ENTRY(interrupt)
 #ifdef APIC
 	cmpl	$255,%eax		/* was this a spurious intr? */
-	je	_no_eoi			/* if so, just return */
+	jne	1f
+	ret				/* if so, just return */
+1:
 #endif
 	cmpl	$CALL_SINGLE_FUNCTION_BASE,%eax		/* was this a SMP call single function request? */
 	je	_call_single
 
 	subl	$24,%esp		/* Two local variables + 4 parameters */
 	movl	%eax,S_IRQ		/* save irq number */
+
 	call	spl7			/* set ipl */
 	movl	%eax,S_IPL		/* save previous ipl */
 
-	movl	S_IPL,%eax
-	movl	%eax,4(%esp)		/* previous ipl as 2nd arg */
-
-	movl	S_RET,%eax
-	movl	%eax,8(%esp)		/* return address as 3rd arg */
-
-	movl	S_REGS,%eax
-	movl	%eax,12(%esp)		/* address of interrupted registers as 4th arg */
-
-	movl	S_IRQ,%eax		/* copy irq number */
-
-	shll	$2,%eax			/* irq * 4 */
-	movl	EXT(iunit)(%eax),%edx	/* get device unit number */
-	movl	%edx,(%esp)		/* unit number as 1st arg */
-
-	call	*EXT(ivect)(%eax)	/* call interrupt handler */
-
-	movl	S_IPL,%eax		/* restore previous ipl */
-	movl	%eax,(%esp)
-	call	splx_cli		/* restore previous ipl */
-	cli				/* XXX no more nested interrupts */
-
 	movl	S_IRQ,%ecx		/* restore irq number */
 
 #ifndef APIC
@@ -114,12 +95,33 @@ ENTRY(interrupt)
 #else
 	cmpl    $16,%ecx		/* was this a low ISA intr? */
 	jge     _no_eoi			/* no, must be PCI (let irq_ack handle EOI) */
-_isa_eoi:
 	movl	%ecx,(%esp)		/* load irq number as 1st arg */
 	call	EXT(ioapic_irq_eoi)	/* ioapic irq specific EOI */
+_no_eoi:
 #endif
+
+	movl	S_IPL,%eax
+	movl	%eax,4(%esp)		/* previous ipl as 2nd arg */
+
+	movl	S_RET,%eax
+	movl	%eax,8(%esp)		/* return address as 3rd arg */
+
+	movl	S_REGS,%eax
+	movl	%eax,12(%esp)		/* address of interrupted registers as 4th arg */
+
+	movl	S_IRQ,%eax		/* copy irq number */
+
+	shll	$2,%eax			/* irq * 4 */
+	movl	EXT(iunit)(%eax),%edx	/* get device unit number */
+	movl	%edx,(%esp)		/* unit number as 1st arg */
+
+	call	*EXT(ivect)(%eax)	/* call interrupt handler */
+
+	movl	S_IPL,%eax		/* restore previous ipl */
+	movl	%eax,(%esp)
+	call	splx_cli		/* restore previous ipl */
+
 	addl	$24,%esp		/* pop local variables */
-_no_eoi:
 	ret
 
 _call_single: